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July/ August 1982

Volume 2, Number 4

$2.95 (USA)
£1.50(UK)

The magazine for Sinclair users

Jse the DEFine function
ro Construct 3-D Plots

To Explore New frontiers..
Six Games of Outer Space

Sinclair ZX Spectrum:
An In-depth Review

Hardware: More
Power Filtering, E

i .... \

jory,

V 1! *1U
1>V

■iK

,«**

\ ^

«W!W/,

SYN1 2/01/ 194301606 12339 25034
ANDR£W KENNCBV- "
2 CAlUMET AVENUE

WORCESTER

MA 01606

SINCLAIR APPLICATIONS PRESENTS
ROM CARTRIDGES FOR THE IX 81

ROM PACKS

• Eliminate the flustration of loading
cassettes

• Enable long programs without long
load times or extra memory

• Can't be erased, never fail to load

CHARACTER
CARTRIDGE

• 3 on ROM character sets
Program selectable
^per/lower case character set

' Graphics cttsffcqter set
Math/electronics character set
None of the above take up any
user RAM

iWith 512 bytes of user RAM the
' ROM PACK can build a Spanish

or German character set with

and I type characters

USER DEFINED
CHARACTER SETS

• As many as you have RAM for
(512 bytes each)

• Easy-to-use interface for defining
your own character sets

Till October 15, 1982

$24.95!

LUNAR
RAIDERS

• Your mission is to fly over the
surface and knock out the alien
facilities, supplies, and ships
without getting yourself shot down,
or running into mountains

• Left, Right, Fire Controls

• 10 Speeds

ON A 272X192
DISPLAY!

Till October 15, 1982

$19.95!

6502 SOFTWARE
EMULATOR

• Learn 6502 machine language
onyourZX-81

• User manual

• Plus introductory teaching guide
to programming the 6502

• "Executes" 6502 machine code
onyourZX-81

• Call Z-80 subroutines from your
6502 programs

• Limited 6502 Assembler
(Supports all 6502 mnemonics but
no symbols or macros)

• Graphic display of the 6502's
status

• Single step, multiple break points,
7 different break point conditions

• "Fake" I/O and interrupts

Till October 15, 1982

$24.95!

6502 GRAPHIC

HARDWARE

EMULATOR

• All features of the 6502 Software
Emulator

• Plus graphic display of the 6502
chip's hardware status

• Plus introductory teaching guide to
the 6502 hardware

Till October 15, 1982

$34.95!

User's manual for any of the
above - $2.00 each
Teaching guide for software and
hardware emulators • $5.00 each
REFUNDED ON PURCHASE
OF PRODUCT

PRODUCT

USER TEACHING
QTY. MANUAL QTY. GUIDE QTY.

TOTAL

CHARACTER CARTRIDGE/$24.95

$2.00

LUNAR RAIDERS/S1 9.95

S2 00

6502 SOFTWARE EMULATOR/S24.95

$2 00

\ : "

6502 GRAPHIC HARDWARE EMULATOR/S34.95

$2 00

$5 00

SHIPPING AND HANDLING/S4. 50

$4 50

TOT

AL>

NAME_

ADDRESS.

•Requires ZX-81.
Tested on U.S.
Version only.

CITY.

. STATE .

.ZIP.

MAIL TO: SINCLAIR APPLICATIONS SoKgaIo^s'

(404)921-4471

Now available in the US. at the
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ACTUAL SIZE 3X2

THE 64K RAM PACK

• Fully built, tested and guaranteed.

• No additional power supply required.

• Black plastic case no larger than 16K
RAM PACK.

• No wobble problems

• Fully compatible with printer etc.

I he use of this memory is as follows:

8K Sinclair ROM

8 - 16K RAM that is unaffected by

NEW, LOAD, SAVE and can
be used for storing machine
code routines.

16 - 32K BASIC Code, Display file,
Variables, Machine Code

32 - 64K Variables

16K RAM PACK at only $49.95 (£29.95)

including FREE ALIEN ATTACK (7K -M/ code)- value $11.00 (£5.75)

As reviewed in 'Your Computer' -- (March 1982) the leading

U.K. Sinclair Publication. Almost 10.000 units sold in the U.K. so far.

RS SOFTWARF

f . r .^m —# ■ r — <- -* r r i w . i

19 WAYSIDE AVENUE, WORTHING, SUSSEX. BN13 3 JU Telephone: 10903) 65691

- M

Explore the excellence of your ZX81 with a

s = j^i = j^i-i5ii

ftCPlOPAK 64K memory extension for $179.95
Give your diminishing memory more byte.

MEMOPAK 64K RAM $179.95

The Sinclair ZX81 has revolutionized
home computing. The MEMOPAK 64K
RAM extends the memory of ZX81 by a
further 56K to a full 64K. It is neither
switched nor paged and is Directly
Addressable. The unit is user trans-
parent and accepts such basic com-
mands as 10 DIM A (9000). It plugs
directly into the back of ZX81 and does
not inhibit the use of the printer or other
add-on units. There is no need for an
additional power supply or leads.

Description of memory

0-8K . . . Sinclair ROM
8-16K . . This section of memory
switches in or out in 4K blocks to leave
space for memory mapping, holds its
contents during cassette loads, allows
communication between programs, and
can be used to run assembly language
routines.

16-32K . . This area can be used for
basic programs and assembly language
routines

32-64K . . 32K of RAM memory for
basic variables and large arrays. With
the MEMOPAK 64K extension the ZX81
is transformed into a powerful com-
puter, suitable for business, leisure and
educational use, at a fraction of the cost
of comparable systems.

Memory Extent ion Specialists

Memotech Corporation

7550 West Yale Ave . Suite 220

Denver, Colorado 80227

Ph.(303)986-0016

MEMOPAK 16K RAM $59.95

With the addition of MEMOPAK 16K,
your ZX81 will have a full 16K of Di-
rectly Addressable RAM. It is neither
switched nor paged and enables you to
execute longer and more sophisticated
programs and to hold an extended data
base.

The 16K and 64K Memopaks come in
attractive, custom-designed and engi-
neered cases which fit snugly on to the
back of the ZX81 giving a firm connec-
tion.

Free service on your MEMOPAK

Within the first six months, should any-
thing go wrong with your MEMOPAK,
return it to us and we will repair or
replace it free of charge.

><—

Memotech Corp. 7550 W. Yale Ave.

Try MEMOPAK with no obligation

You can use our MEMOPAK in your
home without obligation. After 10 days
if you are not completely satisfied,
simply return it for a full refund.

Coming soon .....
A complete range of ZX81 plug-in
peripherals:

MEMOTECH Hi-Res Graphics
MEMOTECH Digitising Tablets
RS232 Interface
Centronic Interface and
Software Drivers

All these products are designed to fit
"piggy-back" fashion on to each other
and use the ZX81 power supply.

Further information forthcoming.

Suite 220 Denver, Colo. 8022?

Yes" I would like to try the Memopak I understand that if I'm not complete satisfied.
I can return it in 10 days for a full refund. d-s~* + n*« *

7 Price T <?ty. Amount

D Check
D Visa

D MC

Act. No.
Name

Memopak 64k RAM

Memopak 16k RAM

Shipping and Handling

$ 179.95

$ 59.95

4 95

Exp

Total

$ 4.95

t U.S. Dollars

Street,
City

State

^ip_

SYCO 7^8

The magazine for Sinclair users

i_jn

July/August 1982

Volume 2, Number 4

DEPARTMENTS

4 Letters

1 SYNC Notes Grosjean

I 2 Try This Berggren, Rainwater

1 4 Just for Fun Boynton, Bush, Grosjean

I D Perceptions Omstein

TheZX81 Parser (Part 2)

22 Kitchen SYNC Groupe, Tardiff, Zatkovich

Two to the What?

T4 Hardware Tips ....... Dowell, Hartung, Hornung, Ingle

Ear Input Circuit, Top Line Hook, Power Filtering, Strong
KBD Signals, ROM Changing, Memory Expansion Power,
Thick Black Bars

I O Resources

80 Index to Advertisers

HARDWARE

JO Double Your Memory Schneider

ZX81 internal RAM upgrade

MATH

43 Understanding Floating Point Arithmetic Logan

Part 3

PROGRAMMING TECHNIQUES

64 DEF on the ZX81 Passler

Translating other Basics

68 Handling Strings from Another DIMension Berggren
ZX80 abilities; game

SYNC IN OUTER SPACE

48 ZX Destroyer Fowkes

Alien attack in a fast action Basic and MC game

60 Galaxy Invaders Gervals

Reflex challenge from outer space

61 Micro Invaders Smith

Small aliens; small ships

62 Comet Crusher Dawson

Smash a fragment; save a city

63 Crossing the Asteroid Belt Hampson

Dodge the asteroids

72 Alien Treasure Chandler

Gather before the alien monster gets you

REVIEWS

£.0 Understanding Your ZX81 ROM Keeney

Book review

30 Sinclair ZX Spectrum Tebbutt

Hardware review

Staff

Managing Editor
Contributing Editor
U.K. Correspondent
Secretary
Art Director
Assistant Art Director
Typesetters

Financial Coordinator
Personnel and Finance
Circulation

Advertising Sales Manager

(V<f WBt o

Paul Grosjean

David Ornstein

Martin Wren-Hilton

Elizabeth Magin

Susan Gendzwil

Diana Negri Rudio

Karen Brown

Renea Cole

William L. Baumann

Patricia Kennelly

Francis Miskovlch

Carol Vita

Jim Beioff

Volume 2, Number 4

SYNC (USPS: 585-490: ISSN: 0279-5701) is published bi-
monthly by Ahl Computing, Inc., a subsidiary of Ziff-Davis Pub-
lishing Company. David Ahl, President; Elizabeth B. Staples, Vice
President; Selwyn Taubman, Treasurer; Bertram A. Abrams, Sec-
retary. 39 East Hanover Avenue, Morris Plains, NJ 07950. Second
class postage paid at New York, NY 10001 and at additional mail-
ing offices.

Subscription rates: USA: One year (6 issues), $16; Two years (12
issues), $30; Three years (18 issues), $42. Canada: $3 per year
additional. Other foreign: $5 per year additional.

For SYNC advertising information, contact Jim Beioff. S YNC Advertis-
ing Sales Manager, Ziff-Davis Publishing Company. One Park Ave.. New
York, NY 10016 (phone 212/725-4216).

Al! other correspondence should be addressed to: SYNC, 39 E. Hanover
Ave., Morris Plains, NJ 07950. In U.K.. SYNC, 27 Andrew Close, Stoke
Golding. Nuneaton CV136EL.

Postmaster: Send address changes to SYNC. PO Box 789-M. Morristown.
f%0.

fill

Photos from Star Trek //. The Wrath of Khan courtesy of Bruce Birmelin/Paramount Pictures.

July/August 1982

LSCROLL

Dear Editor:

For entering machine code routines like
LSCROLL (SYNC 2:2) it is helpful to use
the 8K ROM's string concatenation abili-
ties. The procedure involves breaking up
the one long string in line 10 into a series
of shorter strings which are entered line
by line.

Set the lines up as follows:

10 LET D$= "(begin entering mc num-
bers)"

20 LET D$=D$+"(continue entry)"

30 LET D$=D$+ "(continue entry)"
etc.

Thus each new line includes all the
preceding lines, and we end up with the
whole string from the short strings. This
makes it much easier to correct the
entries since each line can be individually
EDITed.

Also, the following lines give several
advantages in SAVEing:

1 GOTO 3

2 SAVE "name of program"

You now do not have to type in SAVE
every time when you want to make sev-
eral SAVEs. Simply type in GOTO 2.
The program will SAVE itself, then RUN
itself. If you want to make more than one
SAVE, you must change the last character
of the name of the program to normal
video from inverse (for some reason, the
system does that).

The real advantage comes when
LOADing because the program will now
start itself!

I have two other hints. DATA state-
ments could be simulated using strings;
the 8K's VAL function could be used to
remove VALues. It usually makes enter-
ing MC easier to show a zero as with a /
through it.

Erik Sawyer
1213 Patriot Dr.
Siideil, LA 70458

Dear Editor:

Douglass Sharp's LSCROLL program
(SYNC 2:2) is a very useful expansion of
the ZXSTs graphics capabilities. As writ-
ten it requires the 16K RAM, but a few
modifications allow LSCROLL to perform
its magic with the 2K RAM since it

occupies only 172 bytes. (The numbers
correspond to the steps in the original
article.)

1) Rather than have D$ take up val-
uable space within the LSCROLL pro-
gram, enter DS first without a line number
as follows:

LET D*= "3AFE47FE16DA61473E0 n

LET D*=D*+" 032FE473AFF47D600CA7147FE15D2714'
LET D*=DS+" 7C376473E1632FF47F53AFF4747F13AF'
LET D*=D$+" E4780FE16DA954726002E163AFE474F0*
LET D*=D*+" 600ED427D32FF47ED5B0C400EFFF53AF '
LET D*=D*+" E476FF 1 26000600 1AFE76CAAF4713C3 A'
LET D*=D*+" 5470CA7E5ED42E1CABC4713C3A547060 '
LET D*=D*+ " 0F53AFF474FF 1 C5D5E 1 237EFE76C2C74 '
LET D*=D*+" 7E5A7ED522B7D4DD600E1C2E047E5D1C '
LET D*=D*+ n 3F5473DC2E84713C3F14706000B13D5E ,
LET D$=D*+ U 123EDB03E001213C10B79D600C2C447C '
LET D*=D*+" 90000"

These lines have the same length as
those in Figure 1 in LSCROLL, but the
entries have been changed to conform to
the addresses appropriate to the 2K RAM.
Furthermore, the arrangement makes
checking the entries easier.

Enter lines 4 and 20-80 as in Figure 1
but change the address in line 50 to 18259.
Then add:

10CLS

90 STOP

100 SAVE "LSCROLL"

1 10 PRINT "GOTO 4 (TO RUN)"

2) SAVE by entering GOTO 100
(NEVER use RUN with this program for
it will erase D$).

3) Enter NEW.

4) Enter POKE 16388,84 and POKE
16389,71. Enter NEW.

5) LOAD "LSCROLL" and then enter

GOTO 4 (as the screen reminder indi-
cates). In a few seconds the number 21093
will appear. If it does not, check for an
error in D$.

To execute, use RAND USR 18260. To
change the values of XX, YY, and CC
(Figure 3), POKE the appropriate values
into 18430, 18431, and 18418 respec-
tively.

Figure 5 should be corrected as fol-
lows:

7F66 with 32614, not 32615
7F95, not 7FA5, with 32661
7FB4, not 7FC4, with 32692
7FE5 with 32741, not 32740

Harold Miller
Mountainview
Route 3
Clarkesville, GA 30523

SYNC Magazine

Software Breakthrough!

* ZX-Man

$14 96

* Joystick

$14 95

*16K Sinclair
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* Keyboard

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full-size assembled
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7) ZX80 and ZX81 compatable

8) 16K Required

THE INNOVATORS
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Call or Write for more information

American Express, Visa, Master Charge, Money order, pc (allow 2-3 weeks to clear)

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Illinois residents please add 5% III. sales tax

Visit our Showroom 10:00 - 6:00 Monday thru Saturday
MICROCOMPUTERS PLUS, INC.

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PHONE: (309) 342-9572

Cards

Welcome^

master charge,

Flag Use

Dear Editor:

I just saw a copy of SYNC 2:1 with
Philip Gervais's tip on flag use:

100LETA = ABS(A-1)
A simpler and shorter statement to do the
same thing is

100LETA=1-A
Keep up the good work; I enjoy the
magazine.

David Schultz

Total Information Services, Inc.

PO Box 921

Los Alamos, NM 87544

Dear Editor:
An easier way to change a flag is
LET A = NOT A
This is also 10 bytes shorter,

Tim Goldingham
11 Furze Piatt Rd.
Maidenhead SL6 7ND
United Kingdom

Key and Token
Expressions

Dear Editor:

As Richard W. McDaniel points out
(SYNC 1:6), the use of key and token
expressions in PRINT and REM state-
ments can save typing time and memory.
There is, however, another way to insert
these into a program which is sometimes
easier.

Entering THEN gets the ZX80 and
ZX81 into condition to accept keystrokes
as tokens. Suppose that you want to
define A$ as "STOP SEEING YOUR
NAME IN PRINT FOR THE NEW
YEAR". You would key it in as follows:

10 LET A$ = 'THEN STOP (delete
THEN) SEEING YOUR NAME IN
THEN PRINT (delete THEN) THEN
FOR (delete THEN) THE THEN NEW
(delete THEN) YEAR"

This is easier than it looks. The
"DELETE THEN" procedure uses only
three keystrokes: backspace (shifted 5),
delete (shifted 0) and forward space
(shifted 8).

Basil Wentworth
1413EIlistonDr.
Bloomington, IN 47401

Hams and the ZX81

Dear Editor:

I am a delighted ZX81 owner. I am
also an amateur radio operator (ham).

Rather than trying to communicate
with other ZX81 owners by newsletters. I
would be interested in comparing notes
more directly: I propose to organize a
ZX81 network on radio. This would entail
deciding on the frequency, day of the
week, and time of day. After this we
would conduct our regular communica-
tions on a conversational basis.

Other combination radio amateur oper-
ators and ZX81 users are asked to contact
me so that we can get organized soon.
And, if you have a "ham" on the SYNC
staff, it would be wonderful if he would
meet with us on the air to field some of
the questions which are sure to arise!

Dean Sturm. K8CYW
1823 Enslow Blvd.
Huntington, WV 25701

Ed. — We do not have a "/iam" on our
staff, but we have heard from some
operators interested in combining these
two interests. One ZX81 Ham network is
already organized and publishes a news-
letter QZX (contact Martin Irons, K2MI,
46 Magic Circle Dr., Goshen, NY 10924,
for details). We would appreciate hearing
of any others.

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Automatically save on tape.

SALES FILE

Will hold up to 125 products with their wholesale and retail prices

Separates and totals wholesale and retail prices and shows the amount of profit in

up to 25 different accounts

Records inventory automatically or may be changed manually

Keeps a running total of sales tax

Has a cash register mode which will identity, total and add sales lax while it

automatically does your bookkeeping

***A must for any small business."* $19.95

CHECKING;

Lists up to 30 deposits showing amount of deposit and date entered

Lists up to 100 checks and displays check number, date and to whom check was

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Lists by account the total of the checks written to any given account Keeps a

running total of checks written and the balance left m your account

""Great for tax records.*" 59 95

MAILING LIST

Holds up to 1 00 names, addresses and telephone numbers

Search by name, city, zip code, or phone number to find any address or phone

number quickly

Lists all names

Changes or deletes

'"Christmas cards are a snap with this program."* $9.95

INVENTORY (1)

May be used for everything Irom keeping an accurate inventory for your business

to your personal record collection

Holds up to 1 50 items with comments for each

Comments may be used for serial numbers, dates, prices or location

List all items, search for a single item, change or delete any item

'"Every one should have an inventory of household items in case of fire or

,hert ■ $9 95

INVENTORY (2)

Same as above without comments

"'Holds 300 items .""

$9.95

Three $9 95 programs for $24 95

Add $1 00 per tape shipping

Send certified check or money order to

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950 EAST 52 SOUTH
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SYNC Magazine

For the first time—
AVAILABLE

IN THE USA!

4 NEW Handbooks for

your Sinclair ZX-81 or

Timex-Sinclair 1000!!

************

*******************

MASTERING MACHINE CODE
ON YOUR ZX-81

by Toni Baker

Until this comprehensive, veteasv-to-understand, handbook, there
was virtually no material available about the ZX machine code.
Using this guide you'll learn the ins and outs of ZX machine code
translation. Discover the secrets of the ZX-81 , and even see how to
adapt the code to the ZX-80 machine. When you understand the
language translations between BASIC and the ZX machine code,
you'll enjoy the workings of your computer to the utmost!

49 EXPLODING GAMES FOR THE ZX-81

Edited by Time Hartnell

Galactic Intruders. Breakout, Checkers, Death Maze, Star Trek,
Smugglers Mold, and forty-three other favorites are all here, newly
adapted especially for you and your new ZX-8 1 personal computer.
This fascinating gamebook gives vou programming instructions for
all 49 marvelous games PLUS complete and easy-to-understand
game rules. This wonderfully exciting hardcover playbook can be
yours, order below.

******

* * * *

MAKING THE MOST OF YOUR ZX-81

by Tim Hartnell

All new for you and your new ZX-8 1 . this handbook focuses on the
additional features of the ZX-81 . You'll have new games and use-
ful learning tricks, and you'll also see how to write programs that
really work It will guide you through start to finish, using each
feature and function of your new ZX-81 persona! home computer.

THE ZX-81 POCKETBOOK

by Trevor Toms

This handv new programming manual really gets you into ZX-81
functions. Don't just type someone else"s programs . . .now you can
create your ou n and understand why they work. It's fun to learn all
about computing with the ZX-81 POCKET BOOK as a guide.
You'll lee what your new ZX-81 can do, and what extras will make
it abletodoeven more . . , see how to use ZX-81 BASIC in the best
ways . learn to avoid frustration and retvping with program and
data file storage and retrieval techniques— and for ZX-80 owners,
you'll learn how to convert your ZX-80 to the advanced ZX-81
capabilities. And there's so much more! This road map to the ZX-
81 can be yours it's worth every penny'

Using these books you'll be amazed at how fast you'll become a ZX-81 wizard. Of course, if you don't find the books helpful and inter-
esting return them within 15 days for a full refund, and owe nothing.

RESTON PUBLISHING COMPANY c/o

Mail to: PRENTICE-HALL INC., Book Distribution Center

Route 59 at Brook Hill Drive, West Nyack, New York 10995
Please send me my 15-day trial copies of the following titles:

MASTERING MACHINECODE ON YOURZX-81, by Toni Baker, (R4262 3), $18 95

49 EXPLOSIVE GAMES FOR THE ZX 81, by Tim Hartnell, (R2087-6), $16.95

MAKING THE MOST OF YOUR ZX-81, by Tim Hartnell, (R4189-8). $16.95

THE ZX-81 POCKET BOOK, by Trevor Toms, (R9525-8), $16.95

Name

Address-
City

State-

Zip-

WS4*

Now you can charge your orders! Just fill in the information below:
VISA □ □ MASTERCHARGE

account #.
signature-

expiration date-

Save! If check or money order, plus your states sales tax. accompanies your order, publisher pays all postage and handling charges Same money back guarantee applies
Dept V V-0852-W7-(3)

ZX80 ROMs

Dear Editor:

In Michael Rubesch's "4K/8K ROMs
in One ZX80" (SYNC 2:2) the reference
to "pin 28" of the modules rather than to
"pin 28" of the IC socket was a bit
confusing. Later PC boards do have a 28-
pin socket for the ROM while the ROMs
have only 24 pins. Also I have found that
the earlier ZX80 boards have only 24-pin
sockets if they have sockets at all. The
power pin then is pin 24 of the ROM
module which must be inserted at pin 28
of the later sockets.

Robert D. Hartung
POBox 125
Palmyra, NY 14522

Hardware Suggestion

Dear Editor:

In this avalanche of new hardware for
the ZX81 I wonder how many manufact-
urers realize that many of us bought the
ZX81 because it is small. I can put it and
my equally small cassette recorder into a
thin slipcase and use it anywhere a TV is
available. No other low or medium priced

machine offers that degree of portability.
Every manufacturer of hardware for the
ZX81 should keep this in mind and should
include the size of the product in ads. I
favor stuffing as much memory and other
extensions inside the case as possible.

Harold Miller

Mountainview

Rt. 3

Clarkesville, GA 30523

Inventory

Dear Editor:

The Inventory program {SYNC 1:6)
was both enjoyable and useful. Here is an
improvement to SAVE the program (and
variables) as directed by the prompt in
line 2018:

Change line 2020 to:

2020 IF S$-C THEN SAVE
"INVENTORY"

Add:

2019 INPUT S$

2021 STOP

Thanks for a great magazine!

TSGT Chuck Taylor

Diyarbakir

Turkey Si

Brute Birmelin/Paramounl Pictures.

add memory that won't forget! !
EXTEND YOUR ZX81 SYSTEM

d Modify the Sinclair firmware

d Add your own system utilities

n Install permanent machine language
subroutines

□ Up to 8K nonvolatile memory

□ Use 6116 RAM or 2716/2732 EPROM's
d Compatible with 16K RAM packs

COMPLETE KIT:

Plated-through, masked, § silkscreened
pc board; all components, sockets, and
connectors; supplied with a 2K 6116P-3
CMOS RAM (board will accept up to 8K) .
Bare board $15 post paid. Check/money
order (MI residents add 4%) to:

HUNTER 1630 Forest Hills Dr. Okemos

<tAi kQC Michigan 48864 . — .

$214— Pleas e include $1:95 tf)

^™^^ Shipping § handling ^-^

OMNI TEMPLATE

FOR IX -80 and IX -81

WHA T IS OMNI TEMPLA TE?

It is a template program for generating other programs.
While developing programs, our staff needed a collec-
tion of general utilities to avoid the burden of repeating
the same routines over and over. This gave birth to
OMNI TEMPLATE. We found it so effective that we
decided to share it with others.

WHY SHOULD YOU HA VE IT?

It is a great training tool. It helps you to develop a habit
of writing professional-looking programs rather than
rag-tag patch works. It makes programming fun.

WHAT DO YOU GET?

You will receive a cassette tape of OMNI TEMPLATE
Program prerecorded and ready to use. Three addition-
al programs: RACING, INDEX-CARDS and FIT-
POINTS, which were developed by OMNI TEMPLATE,
are on the tape in addition to OMNI TEMPLATE. A
complete listing of OMNI TEMPLATE and a well-
documented manual describing how to use OMNI
TEMPLATE is included.

HO W DO YOU GET OMNI TEMPLA TE?

It is $9.50, if ordered before September I, 1982. It
becomes $ 1 4.50 after that. Please add $ 1 .00 for shipping
and handling. Send money order or check to:

Omni Technology
P.O. Box 10630
Pittsburgh, Pa 15235

PA resident please add 57 cents for PA sales tax.

KAYDE Electronic Systems

ZX80/1

ZX KEYBOARD WITH

REPEAT KEY

Fully cased keyboard $75.90

Uncased keyboard $55.90

Keyboard Case... $21.90

This is a highly professional keyboard using executive buttons as found on top quality
computers It has a repeat key and comes complete in its own luxury case This is a
genuine professional keyboard and should not be confused with toy keyboards currently
available on the market

KAYDE 16K RAM PACKS

The 16K RAMPACK simply plugs straight into the user port at the rear of your computer It is fully
compatible with all accessories and needs no extra power and therefore it will run quite happily on your
Sinclair power supply It does not over-heat and will not lose memory at all As you may know, some
makes go down to 1 1 K after being on for a while

This 16K RAMPACK is very stable and will not wobble or cause you to lose your programme
fully built and tested with a complete money-back Guarantee

I comes

KAYDE FLEXIBLE RIBBON CONNECTOR

Stops movement of RAM PACK and other accessories t^^^W*

(Not needed with a KAYDE RAMPACK) ^ ^S.ft) !

KAYDE 4K GRAPHICS BOARD ^^

The KAYDE Graphics Board is probably our best accessory yet It fits neatly inside you' ZX8V It
comes complete with a pre programmed 2K Graphics ROM This will give nearly 450 extra graphics
and with the inverse makes a total of over nine hundred

The KAYDE Graphics Board has facilities for either 2K of RAM (for user definable graphics). 4K of ROM
or our 4K Tool Kil Chips that will be available shortly All the graphics are completely software
controlled, therefore they can be written into your programmes Here are a few examples A full set of
•pace Invaders — Puckman — Bullets, Bombs — Tanks — Laser Bases and Allen Ships.

NO EXTRA POWER NEEDED

KAYDE 16K GRAPHICS BOARD SOFTWARE

PECKMAN The only true ZX version of the popular arcade game

Centipede In alt I think this is the best presented moving graphics program I've yet seen Phil Garrett

interlace

SPACE INVADERS The best version available anywhere Graphics software can only be used with a graphics board

KAYDE 16K 81 SOFTWARE

Centipede In all I think this is the best presented moving graphics program Ive ^et seen Phil Garratt.

Interlace

3D/3D Labyrinth A Cubit Maze that has corridors which may go left, right, up. down Peckman (the

latest addition in 81 games)

WHY WAIT TO PAY MORE —
FAST t IMMEDIATE DELIVERY

Post to: Dept SY1

Kayde Electronic Systems Ltd

The Conge

Great Yarmouth

Norfolk NR30 1PJ ENGLAND

Tel 0493 57867 (Dept. SY1)

Please pay by

International money order or certified

cheque for immediate delivery.

PImm und me ZX Keyboards with rtpMi key $75.90 ««ch

Pleaeesendme 18KRAMPACKS $59.90 —cb

Pleaee send me Flexible ribbon connectors $25.90 each

Please send me 4K graphics boards $59.90 each

Please send me 16K graphics boerd software $1 1 .90 aach

Please send me NWet software $11.90 aach

(enclose .. __

Name

Address _

Please add $5 p&p for all hardware and $2 for ail software. Please make
cheques payable to Kayde Electronic Systems Lid

5L|nc rotes

Paul Grosjean

SYNC in Outer Space

Space games lead the list of the games
that SYNC receives. This we would
expect since shoot-the-aliens games have
become standard fare in the computer
game field.

Certainly the computer is ideal for
playing such games. As we have seen in
recent years, modern instruments of war
depend heavily upon computer controlled
technology. Hitting the target used to be
the result of an almost intuitive interpre-
tation of a host of variables which was
then put into action by eye/muscle coor-
dination. The most important factor in
hitting the target seemed to be luck —
another name for the unknown or inmea-
sureable variables. The lack of instru-
ments to measure and calculate led to the
use of massive fire power in the hope that
something would hit the target even-
tually.

Now, however, hitting the target is a
matter of computation based on precise
measurement with lasers or radar. Since

space warfare involves speeds, distances,
power, and logistics beyond our exper-
ience, it is necessarily computer warfare.

While the technology was developing
that made space warfare possible, our
imaginations were also being prepared.
Science fiction writers such as E. E.
Smith, A. E. van Vogt, and Isaac Asimov
prepared us to think of conflict between
humans and aliens and between humans
and humans on a galactic scale.

Movie features and serials provided our
imaginations with the visual and sound
effects, The famed radio broadcast of H.
G. Wells's War of the Worlds in 1938
raised conflict with the aliens high in the
national consciousness. Finally TV put
space into every living room. The old
movies were shown again, the new movies
reached larger audiences, and programs
were developed around science fiction
themes, most notably Star Trek. A space
vocabulary has developed and become
part of our daily vocabulary.

We have the building blocks for story
telling, and the computer has become the
means of telling the story, but now the
player participates in unfolding the story.
LET A = (something) is necessary to the
computer, but to the player LET A may
really equal a space ship, an alien, a
minefield, a forest, a castle, a maze —
whatever the imagination desires. A given
computer program can provide a host of
stories without changing a line in it. We
only need to change the terms we assign
to the variables and the relationships we
have instructed the computer to work
out.

In order to simulate some of the un-
knowns of real life, we even introduce
random numbers and elements into the
program. SYNC receives from time to
time games that are purely the "battle of
the random numbers." In general, unless
the program illustrates some significant
programming techniques, these are
rejected because the player's skill and
judgment are vital parts of any satisfying
game. If the player wins, he can claim the
victory for his skill or ability; of course, if
he loses, he can still blame bad luck.

In this issue we have gathered some of
these games into a theme section "SYNC
in Outer Space." We are grateful to
Paramount Pictures for providing photos
from Star Trek II to highlight our theme.

1**$^ FOR YOUR
ZX-81/TIMEX1000

''KEYBOARD BLEEPER— Provides audible feed-
back, improves your keyboard cheaply, fits in-
side. All simple plug-in connections. No Solder-
ing Required. Aids faster more accurate pro-
gramming. All normal and shifted keys bleep in
slow and fast modes. (All 210 characters)
$19.00 includes instructions and postage/hand-
ling.

'LOADING AID — Removes guesswork from ad-
justing cassette recorder volume. Optimum level
attained when red and green LE.D.'s flash in
unison. Plugs-in between computer and
recorder.

$21.00 includes instructions and postage/hand-
ling.

'T-SHIRTS— Black with red lettering "Sinclair
ZX81 ". State size required, 24" — 44".
$7.00 includes postage/handling.

FULCRUM PRODUCTS, DEPT. U
HILLSIDE STEEP LANE
FINDON, W. SUSSEX, ENGLAND
BN14 0UF

COSMONICS

ZX81 HARDWARE/SOFTWARE EXTENTIONS

CS 17 Cassette Read/Write Utilities. Allows the user to
selectively read & write strings and arrays to a cassette,
which can be used by the same program or a different pro-
gram.

CS 17 cassette $20.00

CS 21 Software for TTL Serial Output Port. Provides cor-
rect RS232 timing; provides Sinclair character set transla-
tion to ASCII.

CS21 .cassette $10.00

*CH 21 Complete Plans for 2 IC Serial Output Port for ZX81 .

CH 21 plans $10.00

*CH 21 K 2 IC Serial Ouput Port Kit for ZX81 (complete
plans and parts)

CH21K kit $15.00

CS 22 Software for Serial Input. Provides RS232 input tim-
ing and provides ASCII to Sinclair character translation.

CS22 cassette $10.00

*CH 22 Complete Plans for ZX81 Serial Imput Port.

CH 22 plans $5.00

CH 24 Complete Plans for RS232<— 3> TTL Level Converter.

CH24 plans $10.00

CH 46 46 pin edge connector for ZX81.

CH 46 connector $ 8.00

All cassette software listed here requires a minimum

of 2K RAM

'Note: Any modification made on the ZX81 may

invalidate the Sinclair warranty.

Please add $1.50 postage and handling with each

order.

California residents add 6% sales tax.

COSMONICS, Box 10358, San Jose, CA. 95157

SYNC Magazine

WANT TO FIX YOUR SINCLAIR? ADD MORE MEMORY? ADD A BUSS? WE GOT YOUR PARTS.

We carry all the parts you need to repair your Sinclair with the exception of the Sinclair Logic Unit, the ROM,
and the Printed Circuit Board. In addition we carry OK. WELLER. and XCELITE tools. HAMMOND, and PAC TEC
cases and VECTOR breadboarding and prototyping supplies. We stock resistors, capacitors, integrated circuits,
descrete solid state devices, switches, sockets, connectors etc. etc. Below is a very small sampling of our products.
If you see what you need give us a call, if you don't write for our free catalog.

INTEGRATED CIRCUITS
VOLTAGE REGULATORS

-4*

POSITIVL
7805 +5V
7812 +12
7 815 +15
7824 4 24

NEGATIVL
7905 SV
791 2 12
7915 1 *>

1.25 1. 1.

HEAT SINK 25«

LM323K

3AMP

HEAT SI NK 75«

5VOLT
3.95

C.P.U. & SUPPORT

Z80A CPU 9.45

Z80A PIO 7.65

Z80A CTC 7.65

Z80A DMA 19. 9 5

Z80A SIO/2 23.95

MEMORY

2114 1KX4 STATIC 4.00 3/28.00
4118 1KX8 STATIC 8.25 8/58.00
6116 2KX8 STATIC 14.95 8/125.00
4116 16KX1DY IMAM 3 50 8/24 00
2716 2KX8 EPROM 12 00 8/84 00
2732 4KX8 EPROM 19.95 8/135 00

TTL

PARTIAL LISTING

7400 24 74LS00 25

7403 .24 74LS03 25

7409.... .28 74LS09, 30

7490 .35 74LS90 45

74148... .75 74LS1 38... .70

74154.. 1.25 74LS154.. 1.7 5

74190... 75 74LS1 90... .85

74LS244 1.00 74LS245.. 1.7 5

CMOS

PARTIAL LISTING

74C00 40 4001 30

74C02 A .0 401! 3C

74C30 .40 4016.... 60

74C90.... 1.35 4020... 1.20

74C1 54.. 4.25 407 1 30

74C240.. 2.35 4511... 1.15

74C244.. 2.35 4553... 3.95

LINEAR

MC3401 QUAD OP AMP 50

MC1555 TIMER _ .45

BI-FET OP-AMPS LOW NOISE

SINGLE TL081... .75 TL071 .. .90

DUAL TL082. 1.25 TL072.. 1.50
QUAD TL084.. 2.25 TL074. 2 50

FULL-SIZE KEYBOARD

INCREASE YOUR COMPUTING
TIME BY DECREASING TYPING TIME
ADD A FULL-SIZE KEYBOARD TO YOUR
ZX 80/81 OR MICROAGE. YOUR FINGERS
WILL LOVE YOU FOR IT.

GOLD CONTACTS

WIRE WRAP OR

SOLDER TAIL

5/50

OUR KEYBOARD HAS 62 KEYS SO YOU CAN
ADD LOTS OF EXTRA FUNCTIONS. WE WILL
EVEN SEND YOU PLANS ON HOW TO ADD
SUCH USEFUL THINGS AS AUTOMATIC SHIFT
ON CERTAIN FUNCTIONS. AUTOMATIC REPEAT
AND RESET. EACH KEY HAS GOLD CONTACTS
AND IS FIRMLY MOUNTED TO A BLACK METAL
PLATE WHICH MEASURES 15-1/2" BY 4' AND
DOUBLES AS AN ATTRACTIVE FACE PLATE.
BEST OF ALL YOU CAN GET YOURS IN KIT
FORM, COMPLETE WITH INSTRUCTIONS. OR
WIRED AND READY TO GO EITHER WAY WE
WILL INCLUDE THE EXSFANSION PLANS.

KEYBOARD KIT 34.95 WIRED & TESTED .49.9 5

YOUR
ULTIMATE POWER SUPPLY

WHY WASTE TIME BUILDING NEW POWER
SUPPLIES WHEN YOU WANT TO EXPAND?
BUY AN ULTIMATE SUPPLY AND SPEND
ALL YOUR TIME ON PROJECTS NOT P.S.

MULT1 VOLTAGE
FOR DYNAMIC RAMS ETC.
INPUT _ 1 20 - 220 VAC

OUTPUTS +5VDC--5AMP

+ 1 2VDC =1 AMP
- 1 2VDC-1 AMP
1 2VAC-! /2 A.

SJ/4X/-1/2X4 H MOD CPS-59 50.00

PARTS & PLANS TO CONVERT 12VAC TO

+ 24 FOR EPROM PROGRAMING ADD. -5. 00

SINGLE VOLTAGE
FOR CMOS & TTL LOVERS
INPUT 120- 220 VAC

OUTPUT +5VDC -9AMP

DIM. 91 /2 X 5 X 5

MOD CPS-169. 50.00

ALSO AVAILABLE
5VDC-3AMP MOD SPS 30-5... 24. 95
5.8VDC-1 .2AMP MOD SPS 1-5 5.95

1 20 IN
12 IN

SINCLAIR
CONNECTOR

R. F.
MODULATOR

USA VHf- 5.9 5

DATA

CASSETTES

10 for 15
M*d4 ''). Daiapo.ni
by Mated

high strength sheii

•

JOYSTICK

4 1QK Linear pots

1 V2 metal handle

2 V8 square

S5.95

SOLDER

KESTER 60 40

Rosin core 020 dia

1 Pound Roll

IC SOCKETS

»PI N

SOL

.20

.65

1 4

.25

.70

1 6

.30

.75

1 8

.36

.95

.40

'.10

.45

1 .20

.50

1.25

1.70

.75

1.95

SOLDERING IRONS

WFI I FR

WP25 120V 25W 17.03

WP40 120V 40W 20.93

PENCIL THIN IRON (NOT SHOWN)

WM 1 20 1 20V 1 2W 1 9.47

SOLDERING TOOL STAND

STAND WITH SPONGE,
BASE & RECEPTACLE.

FITS WP-25 WP 40 W-60
MOD PH-60 10.14

FITS WM-1 20
MOD PHM-120.

WIRE WRAP WIRE

K Y N A R #30 WIRE WRAPWIRE

PRECUT TO LENGTH THEN |"
STRIPPED FROM EACH END.

WE GOT IT IN RED, YELLOW,
BLUE, BLACK. WHITE & GREEN

LENGTH 100/BAG

1 000/BAG

3.0" 1.45

7.50

3.5" 1 s*

S.25

4.0" 1.65

9.00

4.5" 1.75

9.75

5.0" 1.85

1 0.25

ADD'L 0.5" UP TO A

TOTAL

OF 1 0.0" .1

.75

#30 BY THE SPOOL

100' ...3.95 500'

..1 1 .95

1000" ,.,19.

HOBBY WRAP TOOL

AUTO-INDEX — |j* Wk\

ANTI-OVERWRAP

MODIFIED WRAP

TOOL WITH BIT
BW26 30B 27.9 5

HAND WRAP TOOL

WRAPS AND UNWRAPS
BUI LTIN#30 WIRE STRIPPER

WSU3 0...JREGULA.R .7.2 5

WSU30M MODIFIED ...8 25

DESOLDERING PUMP

EASY ONE HAND OPERATION

ALL METAL CONSTRUCTION

REPLACEABLE TEFLON TIP

REGULATED SUCTION

DSP' 1 1 85

VACUUM VISE

VACUUM BASED
LIGHT DUTY VISE
1-1 /2" WIDE JAWS
1-1 /4" TRAVEL

VV1 4.1 5

INSERTION/
EXTRACTION TOOLS

INS14I6 INSERT TOOL 4.35
MOS SAFE INSERT TOOLS

MOS1416 14-16 PIN 9.95

MOS2428 24-28 PIN 9.95

MOS40 36-40 PIN.... 10.95

EXTRACTION TOOLS

EX1 14-16 PIN I .49

EX2 24-40 PIN 9 95

WK7 COMPLETE KIT ...3 7.9 5

CLIP AND STRIP

CUT AND STRIP#30
WIRE IN ONE OPERA-
TION. TAKES A LOT
OF THE WORK OUT
OF WIRE WRAPPING.
CAS1 30 2.29

TERMS

Check, money order, VISA, or
Master charge. Add $3,00 for
shipping and handling. Texas
residents add 5% state sales tax.
Foreign orders add $10,00 lor
shipping. U.S. tunds only.
Limitea quanities on some items.

ALTEX ELECTRONICS

618 W. Sunset
San Antonio, Texas
78216

1-512-828-0503

tru tni!

"Try This" features short programs to
show off your computer, impress your
family and friends, and tickle your imagi-
nation when SYNC arrives at your place.
Send your contributions to: Try This,
SYNC, 39 E. Hanover Ave., Morris Plains,
NJ 07950.

4K ROM

Type in the following program. Then
RUN and NEWLINE. Type in any char-
acter or symbol when the quotation marks
appear and hit NEWLINE again. Observe
the results. Repeat until you get back to
program. Note the program.
Our thanks to:
Ken Berggren
104 Ridgeway Ave.
Louisville, KY 40207.

5 PRINT 1

10 POKE 1B4-2'

15 DIM ftfSJ

20 LET B=1£Q

25 INPUT C$

30 GOTO S

SK ROM

Type in the following program. Then
hit RUN and ENTER. Observe the results.
If you like, you can substitute other
characters in the print statements in Lines
20 and 50.
Our thanks to:
Ross A. Rainwater
305 Regal Drive
Lawrenceville, GA 30245

'***'

'•***■

I® FOR X=10 TO IS

15 SCROLL

20 PRINT T^B IX> J '

30 NEXT X

4-0 FOR X = 1S TO 10 STEP

4-5 SCROLL

50 PRINT TftB (X) , '

60 NEXT X

70 GOTO 10

5 PRINT 1

1® POKE ^16427) ,1

15 DIM RfSO

a© LET B=1SS

25 INPUT C$

30 GOTO 5

Bruce Birmelin/Paramount Pictures.

SEEK OUT AND

CAPTURE THE

LANGUAGE OF MAN!

Battlefield:

a 24x32 grid

Opponents:

up to 26 characters of the
alphabet

Weapons:

your mind and the invincible

cursor

Strategy:

to render your opponents

powerless by capturing them
with the cursor. Caution! To
recross your path is to abort
the mission!

Also available:

Life, a simulation of biological
systems, with a high speed
48x64 graphic palette.

Both well-documented games are written in
machine language for the ZX81 with 16K.
$9.95 each. Order by phone or mail. Watch for
exciting new developments coming soon from

NON TRIVIAL SOLUTIONS

Quantity

Price

Total

LETTER
RAIDERS

LIFE

□ Check enclosed. Charge my □ Mastercard □ Visa

Card No. Exp. Date

Signature _

MS TRIVIAL HUITUIR

P.O. Box 2941
Amarillo, Texas 79105
806/376-5723

SYNC Magazine

SOFTSYIMC,

TS 1000 & ZX81 SOFTWARE!

HANG
MAN

f/Vi

Remember wher, you played Hangman as a child? We've created a learning tool for you!
and your children which contains 7 versions of Hangman on the ZX81

Your child can play against the computer's 5 pre-recorded libraries of categorized words,
(each word up to 1 7 letters) Animals, Science, Countries of the World. States of America, and
Fruits and Vegetables,

As a special feature during the game, each program will pick a word from its own library,'
then compare it with the last 50 words played so you will not get repeat words for at leastan
hour of play. Also the computer keeps a running account of how many words you get right
and wrong.

In the 6th version, you or your child may also play against an opponent The computer
requests players names, keeps score and generates the Hangman graphics.

The seventh option allows you to create and save your own versions with up to 500 words
each. This is ideal for parents to create special spelling drills for their children.

Hangman is a great spelling and vocabulary tool for youngsters 6-12 years old, although
its the kind of game adults have been known to indulge in too

16K $14.95

SUPERMAZE

SUPERMAZE is a three-dimensional maze program with
extraordinary full screen graphics that challenges you to
work your way through a complex labyrinth of corridors
Enter SUPERMAZE at your own risk and carefully choosethe
right combinations of passageways to reach the end in the
fewest possible moves

This graphically illustrated adventure game is full of
hazards to impair your ability to get through it. For example as
you wander through the endless corridors, you have to be
careful because there are hidden trap doors you can fall
through, finding yourself in another part of the maze

But SUPERMAZE also features some helpful devices to aid
your journey You can have a compass to guide you or stones
to drop along the way to let you know if you have already
passed through a section of the maze

Written with many machine code subroutines,
SUPERMAZE allows you to choose from ten mazes of
increasing difficulty In addition you can create and store
mazes of your own design

At the beginning of the program, you are given a choice of
options to play including:

• A map option to see where you've been but not where
you are going

• An option to find and take with you gold bars in the maze
This helps you to develop skill in maneuvering

• Stones to drop along the way

• Optional randomly placed trap doors

• The compass to guide you

16K $14.95

ROAD TO RICHES

People have always said, "If only I had some money to play
with, I could turn it into a fortune I could be rich'" Well this is
your dream come true -- an opportunity to show your
prowess at making wise investments because you have just
been given a million dollars -- to play with'

Can you turn it into ten million 9 Or will you lose it all on a
nsky investment? It's up to you

ROAD TO RICHES is an entertaining and educational
computer game in which up to four players are given
opportunities to invest in business ventures in an attempt to
increase their assets

The program simulates a fast-moving world of investment
in which you are confronted with all kinds of investments
ranging from conservative real estate opportunities to highly
risky Broadway shows

The program carefully weighs the risk of each investment
and your chances for winning or losing Like real life, low risk
usually means (but not always) low yield while high risk can
mean hitting the jackpot or financial disaster

Some investments give you more working capital while
others give you equity with annual returns

Pit yourself against a wheeler-dealer and see if. over a
period of seven years, you can come out on top ROAD TO
RICHES is fun and informative, realistically portraying the risk
and skill of high finance

*16K $14.95

PLUS MANY MORE ZX81 PROGRAMS)

WRITE FOR FREE CATALOG

Please send me:

copies of HANGMAN® $14.95 ea

copies of SUPERMAZE® $14.95 ea

copies of ROAD TO RICHES

@ $14.95 ea charge to

Please indicate method of payment — O VISA/ Bankamen card
O Check, money order (no cath please) D Mastercharge
No Exp date

Signature .

Add $1.50 shipping and handling.
New York residents add sales tax.

SEND CHECK OR MONEY ORDER TO:

SOFTSYIMC, U\IC

PQBgk48Q Murray Hill Station, r^ew^rtxk, NY 10156 (212)685-2080

NAME

ADDRESS

CITY

STATE/ZIP

8K ROM; IK RAM

just Far pun

Generally SYNC prefers articles in some
depth to help you get more out of your
computer. However, we receive many
short programs that illustrate a point,
demonstrate a technique, or show some-
thing the reader has found interesting.
"Just for Fun" shares these programs with
you. If you learn something, great. If you
have some fun, great. If you have some
that you want to share, send them to: Just
for Fun, SYNC, 39 E. Hanover Ave.
Morris Plains, NJ 07930.

Graphics Loop I

Bernard Bush

One technique for squeezing more into
the limited memory iri the basic ZXM1 is
to use a loop. The following program
illustrates the method applied to create a
continually changing graphics display. Enter
the program. Then be sure you are in
SLOW mode. Hit RUN and ENTER and
enjoy the show.

REM GRAPHICS LOOP

LET fl=INT

(RND*10) +1

LET B=INT

(RNJ>*10) -el

4-0

LET e=INT

(RND*10> +1

LET D = INT

(RND*10) +1

LET E = INT

(RNP*10) +1

100

• 10

FOR J = l TO

120

PRINT CHR*

130

PRINT CHR$

140

PRINT CHR*

150

PRINT CHR*

160

PRINT CHR*

170

NEXT U

180

UNPLOT U,U

-18

19©

GOTO 10

200

REM STOP WITH BRERK

Bernard Bush. Rt. 2. Mansfield, MO 6S704.

Graphics Loop II

James Grosjean

The same screen display developed in
"Graphics Loop I" can be achieved by
the following program which establishes
the loop through a technique suggested
by Ken Berggren in his "Handling Strings
from another DIMension'm this issue.

18 FOR 1=1 TO 5

20 LET R=RND*9+1

30 POKE 16537.38+1

4-0 NEXT I

50 POKE 16537.36

60 PRINT RT 6 .

70 FOR J = l TO" 58

80 PRINT CHR* PI, CHR* B;CHR* C.

CHR* D. CHR* E;

90 NEXT J

" 00 RUN

James Grosjean. 50 Kings Rd., Chatham, NJ 07928.

Draw It

Robert S. Boynton

Many drawing programs require you to
encode a picture and then display it. but
this short program allows you to draw
and edit a detailed picture even in IK.
Enter the program, be sure you are in
SLOW mode, and press RUN and NEW-
LINE. A black pixel will be displayed at
center screen. You can move the pixel by
using the arrow keys (no need to shift). If
you make a mistake or you want to move
without leaving a mark, press RUBOUT
and the pixel will flash. You can now
move it to a new location or backwards
to erase. Press RUBOUT again to return
to plotting. You can also put any keyboard
character into your picture by pressing
the EDIT key I no shift), and insert the
character you want in the quotation marks.
Press NEWLINE and the character will

appear at the pixel location. The RUBOUT
feature works on the printed characters.
Do not go beyond the normal machine
plotting area or error B will result. If you
do not want to use the characters, you
can omit lines 1 10 and 130 to 150.

20
30
4-0
50
60

6©

LET Z=0
LET X=32
LET Y=22
PLOT X ,

1
1
1

1
100

T 2
110

120
130
140
150

HEN UNPLOT X.Y

THEN LET

IF INKEY*= 5
IF INKEY*="S
IF INKEY*-"&
IF INKEY*s"7
IF INKEY*= "0
INKEV»="1

=X-
=X +
:Y-
=Y +
•HO

THEN GOSUB 13

THEN LET

GOTO 4-0

INPUT R*
PRINT H*
RETURN

Robert S. Boynton. 189 David Humphreys Rd.. Derby. CT 06418.

SYNC Magazine

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The ZX81 Parser (Part 2)

In the last issue I began a discussion of
the ZX8Ts parser which is a complex and
tricky combination of software tech-
niques. In this issue I will continue the
discussion by detailing the main parser
routines.

Syntax Checking vs. Execution

When you enter a line into the ZX81,
the parser is called twice to evaluate it.
The first time is when you hit ENTER
after you have just typed a line into the
system, This call instructs the parser to
check the syntactic correctness of the
line entered. If the line is in error, an S
cursor is placed in the line at the appro-
priate position. The parser then returns
to the keyboard routine to permit the
user to correct his error. The process by
which any syntax error is shown to the
user is simple: an RST 8 instruction is
executed. This instruction is followed by
a byte which specifies the "REPORT
NUMBER". The RST 8 begins execution
by loading X-PTR with the value of CH-
ADD, the system's interpreter pointer (see
the ZX81 BASIC Programming Manual,
chapter 28).

If there are no syntax errors, the parser
returns, and the line is converted into its
internal representation which is shown in
Figure 1.

At this point, one of two actions will
occur. If a line number was specified, the
internal representation will be stored in
the program area. Note that, if the text of
the line is null (i.e., there is no text after
the line number), and if a line number
was given, the old version of the line, if
any exists, will be deleted. If no line
number was given, the parser will be

called again. This time, however, it will
execute the line.

Clearly, some method must exist to tell
the parser whether it should check-syntax
or execute the line passed to it. A bit (bit
7) in the FLAGS system variable is allo-
cated for this use. If the parser is to
execute the line, the bit will be set.
Otherwise (i.e., syntax-check only), it will
be reset. Thus the designation EXEC/
SYNTAX. A routine SYNTAX-Z (0DA6)
is used to check this bit. This routine will
return Z true if just-checking is specified.
It returns Z false (i.e., NZ) if execution is
to occur.

To clarify the use of this flag, let me
give an example. Suppose the parser is
passed the following line:

PLOT 5,10 A
The code that will be executed is chosen
by the parser. This process is detailed in
"The Parser Body" below.

It must be made clear that the process
of fetching arguments and checking
syntax cannot be thought of as disjointed.
In the case of the PLOT command, as is
the case with almost all other commands
which take arguments, all arguments are
passed to Section B on the "calculator
stack." (See "Understanding Floating
Point Arithmetic: The CALCULATOR
Language," by Ian Logan, SYNC 2:2.) As
we will see in the next section, the rou-
tines used to fetch arguments check
syntax, implicitly, as they move CH-ADD
through the line — or rather the routines
used to check syntax and fetch arguments,
implicitly, as they move CH-ADD through
the line.

The Parser Body

The ZXHTs parser is table-driven. This
means that all syntax checking and exe-
cution are directed by a series of tables.

Figure 1: Tke internal representation of a line in Basic.

ENTER

Text of Line

Length of Line (16 bits)

Line Number \ 16 bits)

Listing 1 : The Parser Code.

P-OFFSET:

.BYTE $8B,$8D,$2D,$7F, $81,3^9, $75
BYTE $5F f $40 f $^2 f $2B f $17.$lF f $37
BYTE $52,$45,$0F»$6D,$2B,$^,S2X
BYTE $5A,$3B f $4C i $^5.$0D i $52 f $5A
BYTE $4D,$15,*6A

SYNC Magazine

Listing 2: The Offset Table.

The parser code is given in Listing 1.
There are two entry points into the
parser: LINE-SCAN and LINE-RUN.
When calle d via LINE -SCAN, the parser
sets EXEC/SYNTAX to SYNTAX (i.e..
Ot. and calls E-LINE-NO. This subroutine
is used to check the line number specified.
If the line number is outside the bounds
of a legal line number, a REPORT "C" is
issued. If the line number is valid, LINE-
SCAN falls through to LINE-RUN.

As you probably know, the ZX81 will
accept an expression as the argument to
an INPUT statement. The parser is used
to evaluate this expression. The first
action performed by the parser (entered
via LINE-RUN) is to check whether an
INPUT statement is being executed. This
condition is specified by bit 5 of FLAGX.
If an INPUT statement is currently being
processed, one of the two actions will
occur. If the fir st charact er is a STOP,
and the EXEC/SYNTAX flag = EXEC,
the parser will exit by using RST 8 to
signal a REPORT "D*. If the first char-
acter is not a STOP, then the parser jumps
to INPUT-REP (see CIass-2). If an INPUT
statement is not being executed, a jump is
made to LINE-NULL.

The parser, continuing execution at
LINE-NULL, now checks to see if the line
is null, If it is, the parser returns immed-
iately. If the line is non-null, the parser
checks to be sure that the first character
in the line is a command. Once again, if it
is not, REPORT U C M will be issued.
Assuming that the first character in the
line is a command, the parser continues
by calculating the address of the com-
mand s entry in the parameter table. This
is done by using an offset table (0C29).
The offset table and the paramater table
are shown in Listings 2 and 3,
respectively.

Reviewing the parameter table, you will
see that each command entry specifies
the format of a particular command, For
example, PLOT (0C98) is shown to be
eomprsised of a CLASS-6 item, a comma
(.), and another CLASS-6 item. After
finding the currently executing command
in the table, the parser falls through into
a loop { GET-PARA M), which is respon-
sible for fetching successive parameter-
bytes from the command's entry.

After fetching a byte, GET-PARAM
checks its value. If the byte's value is
greater than OBh. the GET-PARAM loop
jumps to the SEPERATOR routine which
checks the character in the line against
the specified parameter-byte (i.e., or=,
etc). If a match is found to exit,
SEPERATOR returns to the beginning of
the GET-PARAM loop. If the characters
did not match, REPORT "C" is issued via
RST 8.

F-LET:

F-G0T0:

F-IF:

P-GCSUB;

P-STQP:
F- RETURN;
P-FOR:

P-NEXT;

F-FRINT:
P- INPUT:

P-DIMi
r -REM J
P-NEW:

?-R T
P-LIST:

SET-STRLNi

DtTM .

CLASS-2:
QT-REP:

.BYTE $01, $14, $02

BYTE $06, $00
.BYTE $81,$0E

.BYTE $06,$DE,$05
.BYTE $AB,$0

,BYTE $06,$00
.BYTE $B5,$0E
.BYTE $0G,$DC,$0C

.BYTE $00,$E8,$0E

.BYTE $04 , $14 , $06
■BYTE $CF f $G6,$05
.BYTE $B9,$0D

, BYTE
.BYTE

$04, $00
$2E f $0E

.BYTE $05,$CF t $0A

.BYTE $01, $00
.BYTE $£9,$0S

.BYTE $05, $09,314

P BYTE $05,$6A,$0D

.BYTE $00,$C3, :

.BYTE $Q3,$AF,$GE

■BYTE $03,330,307

.BYTE $06, $1 A ,306
.BYTE $00, $92, $QE

CALL NZ.STK-FETCH

LD ML, FLAGX

OR (HL)

LD (HL).A

EX DE.HL

LD (STRLEN),BC

LD (DEST),HL

RET

POP BC

LD A, (FLAGS)

PUSH AF

CALL SCANNING

POP AF

LD BC,$1321

LD D,( FLAGS)

X0R L

.AND $40

Class 1
11 ti

Class 2
Class 6
Class
Addr-$0E8l
Class 6
TlIFi
Class 5

Addr-$0DAB
Class 6
Addr-$0EB5
Class
Addr-$QCEC
Class
Addr-$0ED8
Class 4

Class

Addr-

Class

Addr-

Class

Addr-

Class

Addr-

Class

Addr-

Class

Addr-

$0DB9

30E2E

5
$0ACF

$0EE9

5
$1409

$0D6A

C 1 p. s f

Addr-$03C3

Class 3

Addr-$0EAF

Class 3

Addr-$0?30

Class 6
n it

:iass 6
Class C
Addr~$0E92

July/August 1982

If. on the other hand, the parameter-
byte's value is less than OB, the parser
uses another offset table (0D16) to find
the address of the class handler. The class
handler is then called. When it finishes
execution, it will (probably) return to the
beginning of the GET-PARAM loop.

Class Handlers

A class handler is a routine used to
parse out a particular type of variable
(i.e.. non-constant) parameter from a line.
These items include, but are not limited
to, variable names and expressions. As
class handlers perform extremely diversi-
fied functions, each will be presented
separately with a description of the effects
of its execution.

CLASS-6

CLASS-6 is the routine used to parse
out an integral expression. CLASS-6 uses
a ROM routine known as SCANNING
which is a general expression parsing
routine. Although a discussion of expres-
sion evaluation techniques is beyond the
scope of this article, it suffices to say
that the SCANNING leaves the result of
its evaluation on the calculator stack. It
also sets bit 6 of FLAGS to indicate
whether the value parsed was of numeric
or string type. When control is returned
to CLASS-6. after its call to SCANNING,
it checks bit 6 of FLAGS. If a string
argument was specified, then REPORT
"C" is given. If a numeric argument was
supplied, the CLASS-6 returns.

CLASS!

CLASS-1 is called to parse out an
assignable variable name. This procedure
begins by calling LOOK-VARS, a routine
to pull a variable name out of the source
line. LOOK-VARS returns a pointer
to the variable's record in the VARS
file. If the variable is not found, LOOK-
VARS creates it. and returns a pointer to
the created record. CLASS-1 stores the
returned pointer and other pertinent
information in system variables for later
use. It then returns.

CLASS4

CLASS-4 is a routine used for a purpose
similar to that of CLASS-1. It is used to
parse out the variable name specified as
the argument to a FOR or NEXT com-
mand. It calls LOOK-VARS and checks
the type bits returned in the C register. It
checks to be sure that both bits 5 and 6
are set in the type byte. If they are not
set, REPORT "CT is given. If the variable
name was valid (i.e., a single-character
numeric scalar), CLASS-4 will jump into
the middle of the CLASS-1 routine which
will then proceed by storing the informa-
tion on the variable in the appropriate
system variables.

Listing 2 (continued)

JLASS-4 :

-6:

JRT-C:
: -STK:

>YNTAX-Z i

SEPERATOR:

C-OFFSET:
CHECK -END

CHECK-2 :

REP0RT-C2:
CLASS-3:

CLASS-O:
CLAS3-5:

Call the

calculator
S tk— z er*o
End-calc

JR NZ,REPQRT-C
BIT 7,D

JR NZ, CLASS-END
JRB CHECK-2

CALL LCCK-VARS

PUSH AF

LD A, C

OR $9F

INC A

JR NZ.REPORT-C

POF AF

JR CLASS-^-2

CALL SCANNING
BIT 6, (FLAGS)
RET NZ

RST 8
.BYTE ?0B

JR NZ, CLASS-6
CALL SYNTAX-!
RET Z
RST

.BYTE .
. BYT^ 7 '
RE?

BIT ? f (FLAG£

RET

LD HL, C-OFFSET

LD B f $00

ADD HL,BC
LB C,(HL)
ADD HL,BC
PUSH HL
RET

RST 18

CF C

JR NZ.REP0RT-C2

RST 20

RET

. BYTE $17 , $25 , $53 , $0F , $6B , $13 > $76

CALL SYNTAX-Z

RET NZ

FOP BC

LD A f (HL)

CP NEWLINE

RST Z

JR REPORT-C

CP NEWLINE
CALL N0-T0-STK

CP A

POP BC

CALL Z, CHECK-END

EX DE, HL

LD HL,(T ADDR)

LD C , ( HLj

SYNC Magazine

AARDVARK - THE ADVENTURE PLACE

ADVENTURES FOR OSI, TRS-80, TRS-80 COLOR, SINCLAIR, PET, VIC-20

ADVENTURES - Adventures are a unique
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In Adventuring, the computer speaks and
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Except for Quest, itself unique among Ad-
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Adventures are more like a novel than a comic
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All of the Adventures in this ad are in Basic.
They are full featured, fully plotted adventures
that will take a minimum of thirty hours (in
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Adventuring requires 16k on Sinclair, TRS-
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BASIC.

TREK ADVENTURE by Bob Retelle - This

one takes place aboard a familiar starship and
is a must for trekkies. The problem is a famil-
iar one - The ship is in a "decaying orbit"
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the engines are out (You would think that in
all those years, they would have learned to
build some that didn't die once a week). Your
options are to start the engine, save the ship,
get off the ship, or die. Good Luck.

Authors note to players — I wrote this one
with a concordance in hand. It is very accurate
— and a lot of fun. It was nice to wander
around the ship instead of watching it on T.V.

CIRCLE WORLD by Bob Anderson - The

Alien culture has built a huge world in the
shape of a ring circling their sun. They left
behind some strange creatures and a lot of ad-
vanced technology. Unfortunately, the world
is headed for destruction and it is your job to
save it before it plunges into the sun!

Editors note to players - In keeping with
the large scale of Circle World, the author
wrote a very large adventure. It has a lot of
rooms and a lot of objects in them. It is a very
convoluted, very complex adventure. One of
our largest. Not available on OSt.

HAUNTED HOUSE by Bob Anderson - This
one is for the kids. The house has ghosts, gob-
lins, vampires and treasures — and problems
designed for the 8 to 13 year old. This is a
real adventure and does require some thinking
and problem solving - but only for kids.

Authors note to players -This one was fun
to write. The vocabulary and characters were
designed for younger players and lots of things
happen when they give the computer com-
mands. This one teaches logical thought, map-
ping skills, and creativity while keeping their
interest.

DERELICT by Rodger Olsen and Bob Ander-
son For Wealth and Glory, you have to ran-
sack a thousand year old space ship. You'll
have to learn to speak their language and
operate the machinery they left behind. The
hardest problem of all is to live through it.

Authors note to players — This adventure
is the new winner in the "Toughest Adventure
at Aardvark Sweepstakes". Our most difficult
problem in writing the adventure was to keep
it logical and realistic. There are no irrational
traps and sudden senseless deaths in Derelict.
This ship was designed to be perfectly safe for
its' builders. It just happens to be deadly to
alien invaders like you.

PYRAMID by Rodger Olsen - This is one of
our toughest Adventures. Average time
through the Pyramid is 50 to 70 hours. The
old boys who built this Pyramid did not mean
for it to be ransacked by people like you.

Authors note to players — This is a very
entertaining and very tough adventure. I left
clues everywhere but came up with some in-
genous problems. This one has captivated
people so much that I get calls daily from as
far away as New Zealand and France from
bleary eyed people who are stuck in the
Pyramid and desperate for more clues.

QUEST by Bob Retelle and Rodger Olsen -

THIS IS DIFFERENT FROM ALL THE
OTHER GAMES OF ADVENTURE!!!! It is
played on a computer generated map of
Alesia. You lead a small band of adventurers
on a mission to conquer the Citadel of Moor-
lock. You have to build an army and then arm
and feed them by combat, bargaining, explora-
tion of ruins and temples, and outright ban-
ditry. The game takes 2 to 5 hours to play
and is different each time. The TRS-80 Color
version has nice visual effects and sound. Not
available on OSI. This is the most popular
game we have ever published.

MARS by Rodger Olsen - Your ship crashed
on the Red Planet and you have to get home.
You will have to explore a Martian city, repair
your ship and deal with possibly hostile aliens
to get home again.

Authors note to players — This is highly
recommended as a first adventure. It is in no
way simple— playingtime normally runs from
30 to 50 hours — but it is constructed in a
more "open" manner to let you try out ad-
venturing and get used to the game before
you hit the really tough problems.

NUCLEAR SUB by Bob Retelle - You start
at the bottom of the ocean in a wrecked Nu-
ciear Sub. There ib literally no way to go but
up. Save the ship, raise her, or get out of her
before she blows or start WWII I.

Editors note to players — This was actually
plotted by Rodger Olsen, Bob Retelle, and
someone you don't know — Three of the nas-
tiest minds in adventure writing. It is devious,
wicked, and kills you often. The TRS-80 Color
version has nice sound and special effects.

EARTHQUAKE by Bob Anderson and Rodger

Olsen - A second kids adventure. You are
trapped in a shopping center during an earth-
quake. There is a way out, but you need help.
To save yourself, you have to be a hero and
save others first.

Authors note to players — This one feels
good. Not only is it designed for the younger
set (see note on Haunted House), but it also
plays nicely. Instead of killing, you have to
save lives to win this one. The player must
help others first if he/she is to survive — I like
that.

Please specify system on all orders

ADVENTURE WRITING/DEATHSHIP by
Rodger Olsen — This is a data sheet showing
how we do it. It is about 14 pages of detailed
instructions how to write your own adven-
tures. It contains the entire text of Deathship.
Data sheet - $3.95. NOTE: Owners of OSI,
TRS-80, TRS-80 Color, and Vic 20 computers
can also get Deathship on tape for an addi-
tional $5.00.

PRICE AND AVAILABILITY:

All adventures are $14.95 on tape except
Earthquake and Haunted House which are
$9.95. Disk versions are available on OSI and
TRS-80 Color for $2.00 additional.

ALSO FROM AARDVARK — This is only a partial list of what we carry. We have a lot of other games (particularly for the
TRS-80 Color and OSI), business programs, blank tapes and disks and hardware. Send $1.00 for our complete catalog.

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Phone Orders Accepted 8:00 a.m. to 4:00 p.m. EST. Mon.-Fri.

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loading.

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I isiinji 2 Iconlinued)

CLASS-END:

CLAS3-1:
CLASS-4-2:

REFORT-2:
SET-STK:

LINE-SCAN:
LINE-RUN:

STOP:
LINE-NULL:

SCAN-LOOP:
GET -P ARAM:

INC HL
LD B , ( HL )
EX DE , HL
PUSH BC
RET

CALL L00K-VARS
LD (FLAGX),$00
JR NC, SET-STK
SET l.(FLAGX)
JR NZ.SET-STRLN
RST 8
.BYTE $01
CALL Z.STK-VAR
BIT 6, (FLAGS)
JR NZ.SET-STRLN
X0R A

CALL SYNTAX-Z
LD (FLAGS), 01

CALL E-LINE-N0
CALL SET-MEM
LD HL,ERR_NR

LD (HL),$FF

LD HL.FLAGX

BIT 5,(HL)

JR Z, LINE-NULL

CP "STOP"

LD A,(HL)

JP NZ, INPUT-REP

CALL SYNTAX-Z

RET Z

RST 8
.BYTE $0C

RST 8
.BYTE $08

RST 18
LD B,$00
CP NEWLINE
RET Z

LD C,A

RST 20

LD A.C

SUB $E1

JR C.REP0RT-C2

LD C,A

LD HL.P-0FFSET

ADD HL.BC

LD C , ( HL )

ADD HL.BC

JR GET-PAR AM

LD HL,(T ADDR)

LD A,(HLT

INC HL

LD (T_ADDR),HL

LD BC.SCAN-L00F

PUSH BC

LD C,A

CP $0B

JR NC.SEPERAT0R

j Set up SYNTAX-
checking only

; ie S3 hex

; Error "D"

; Give REPORT "9 1

SYNC Magazine

CLASS-2

The CLASS-2 routine is responsible for
parsing out the value assigned to a var-
iable (previously specified by CLASS- 1)
in a LET or INPUT statement. The
expression is evaluated by SCANNING.
The type of the expression evaluated is
then checked against the type of the
variable (name) stored by CLASS- 1. If
the types are not equal, then REPORT
"C" is issued. If, on the other hand, the
types do mix, a jump is made to the LET
routine at 1321h.

CLASS-5

IF, PRINT, LPRINT. FOR. REM,
LOAD, DIM, and SAVE all have CLASS-
5 as their last parameter. The CLASS-5
byte (05h) is followed by two bytes which
form an address. The address specified is
that of the handler for that command.
The command handler is the routine that
actually performs the action specified by
the command (i.e., placing a dot on the
screen, in the case of a PLOT command).

By reviewing the code for CLASS-5, you
will see that, after POPing its return
address {probably 0CF4h), its gets the
next two bytes from the command's entry
in the parameter tabic. It combines these
bytes and jumps to the address specified
by the resulting word.

Before executing the jump, a CALL is
made, conditionally (if the Z-flag is set)
to CHECK-END. This routine cheeks to
be sure that the next character in the line
specifies an end-of-line (i.e., a NEW-
LINE). If it does not, REPORT "C" is
given. If the character is a NEWLINE, a
return is made.

CLASS-0

CLASS-0 is simply a CP A instruction.
This instruction is commonly used by Z80
programmers to set the Z-flag. After
executing this instruction, CLASS-0 falls
through to CLASS-5. CLASS-5 will then
CALL CHECK-END. as the Z-flag is set.

P-RAUD:

P-LOAD:

P-SAVE:

P-CONT:

P- CLEAR:

P-CLS:

P-PLOT:

F-UNPLOT:

P-SCROLL:
P-PAUSE:

P-SLOWi

P-FAST:
P-COFY:
P-LPRINTi
P-LLIST:

Listing 3: The Parameter Table.

.BYTE $03,$6C,$OE

.BYTE $O5,$i+O,303

.BYTE $05,$F6,$02

.BYTE $00,$?C,$0E

.BYTE $00,$9A,$14

.BYTE $00 f $2A,$0A

.BYTE $06,$1A,$06
.BYTE $00,$AF,$0B

.BYTE $00,$0E f $0C

.BYTE $06, $00, $32
.BYTE $0F

.BYTE $00,$2B,$0F

•BYTE $00,$23,$0F

•BYTE $00, $69, $08

.BYTE $05,$CB,$0A

.BYTE $03,$2C,$07

Class 3
Addr-$0E6C
Class 5
Addr-$03^0
Class 5
Addr-$02F6
Class
Addr-$0E7C
Class
Addr-$1^9A
Class
Addr-$0A2A
Class 6

it ti

Class 6

Class

Addr-$0BAF

Class 6
ti t*

Class 6
Class
Addr-$0BAF
Class

Addr-$0C0E
Class 6
Class

Addr-$0F32

Class

Addr-$0F2B
Class
Addr-$0F23
Class

Addr-$0869
Class 5
Addr-$0ACB
Class 3
A ddr-$0?2C

CLASS-3

CLASS-3 handles the argument speci-
fied after a RAND. LIST, LLIST, or RUN
command. This element can be either a
NEWLINE or an integral expression. If a
NEWLINE is given without any expres-
sion, a default of is assumed, and pushed
onto the calculator stack. If a number
was specified, CLASS-6 is CALLed to
parse the expression. After pushing the
appropriate number onto the calculator
stack, CLASS-6 returns to CLASS-3.
CLASS-3 then falls through to CLASS-0.

In the next issue I will discuss the
command handlers themselves.

Once again, I wish to extend my utmost
gratitude to Ian Logan for his hard work
in disassembling the 8K ROM. All labels
in this article come from the result of his
work: The Sinclair ZX81 ROM
Disassembly, Part A.

Until next time, same relativistic time
period, same non-Euclidian universe. %

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July/August 1982

4K ROM <8K ROM); IK RAM

Mitcnsn sgnc

Alan Groupe, Michael Tardiff, and Ivan Zatkovich

Two to the What?

Recently, a cousin from Lincoinwood,
Illinois, came out to visit. Along with him,
he brought a couple of "extra credit''
problems given him by his eighth grade
science teacher.

One of the problems was to calculate 2
to the 420th power. The problem came
with the following restriction: "You can't
use a computer." Since no commonly
available computer can store a number
this large with perfect accuracy (remem-
ber, floating point numbers are only
approximations of a number), this restric-
tion seemed unnecessary.

You have probably already guessed,
though, that with some thought and a few
tricks, you can solve this problem using a
computer. It should also come as no
surprise that we are going to show you
how to do it on your ZX80/81.

It does seem to us, however, that any
eighth grader who could figure out how
to solve this problem on a computer is
well on the way to becoming a clever
problem-solver who can make good use
of available tools, and, therefore, deserves
the extra credit. Lincoinwood School
District, take note.

To solve this problem on a ZX80/81 or
on any computer, you first have to under-
stand how to do it by hand.

Unless you are a child prodigy, you
cannot handle a number as big as 2 to the
420th either. The best way to deal with
things too big to handle all at once, of
course, is to break them down into "bite-
size" chunks. In this case, the most
obvious method probably would be to
treat each digit separately. You could
take 2, multiply it by 2, take that answer
and multiply it by 2 again, and so on, 419
times. When the numbers begin getting
too large to multiply in your head, you
would move from right to left, multiplying
a digit by 2, adding in any carry from the

previous digit, and carrying into the next,
if necessary. Just like in school, right?

While the ZX80/81 cannot handle
numbers as large as 2 to the 420th, it can
handle numbers as big as 32767 (decimal).
Rather than doing the calculations one
digit at a time, as you would do by hand,
it is a simple matter to have the ZX80/81
multiply four digits at a time. Listing 1
gives the program for calculating 2 to the
420th. This was written on the ZX80 4K
ROM, but it works also on the ZX81 if
you make this change:

180 PRINT A(I );"##";

Since the answer to our problem is 127
decimal digits long (How do we know?
Trust us.), we can store it in an array of
32 integers. This is done in line 10. Lines
20-50 initialize our answer to 1 (2 to the
zero-ith power). Lines 60 through 160 are
the main loop of the program and multiply
A by 2 420 times. C is the carry from one
"digit grouping" to the next and is cleared
in line 70. (There is no carry, of course,
into the rightmost digit.)

Lines 80 and 90 set up a backwards
FOR-NEXT loop going from 32 down to
1 covering each digit group from right to
left. We could have numbered the digit
groups in the other direction, but then we
would have needed a reverse loop to print
out the result, so it did not make much
difference which way we went. Line 100
multiplies the current digit group by 2
and adds in the carry from the previous
digit group. Line 110 clears the carry,
since we do not as yet know whether
there is to be a carry out of the current
digit group. Line 120 skips over the carry
processing if the current digit group is
within range (0-9999). Lines 130 and 140
do the carry processing by bringing the
digit group back within range and setting
the carry into the next group to 1. You
should satisfy yourself that this is correct.

Line 150 closes the loop at line 80 and
proceeds to the next digit group. Line 160
closes the loop at line 60 and proceeds to

the next doubling. Calculations are now
finished, and lines 170 through 190 print
out the result.

Note that the format of the output is
rather sloppy. The reason for this is that
some of the digit groups may be less than
1000, and in order for the result to be
printed together, program lines would
have to be added to print these groups
with leading zeros. While this is not
particularly difficult, it would tend to
make the program more complicated. If
you have sufficient RAM, the inspiration,
and a compulsion for neatness, see if you
can alter our program to "prettyprint. ,,

When run, the program grinds away
for a little over four minutes before
returning with the answer. Compared to
pencil and paper, that is not bad. But
consider this: on the first iteration of the
main loop (lines 60-160) the variable
A(32), which is originally 1, is multiplied
by 2, giving 2. But Ad) through A(31).
while being equal to 0, are still multiplied
by 2. On the second iteration this is also
true. In fact, most of the four minutes are
spent multiplying by 2!

This provides us with a good example
off how careful planning can make a
program run faster. If you think through
a problem ahead of time, you can cut out
the pointless work and free your ZX80/81
to do the real work of calculating or
searching or whatever. Sure enough, there
is a simple way to "optimize" our program
to eliminate the wasted work of multi-
plying by 2.

If you keep a pointer (call it "P") to the
most significant (leftmost) non-zero digit,
and stop the right-to-left multiplication
loop (lines 80-150) at that point, you avoid
the unnecessary multiplications. Remem-
ber, though, to move this pointer to the
left when you carry out of that digit (in
this case, the digit to the left will now be
non-zero).

If that is a bit tough to follow the first
time through, add the lines in Listing 2
for 4K ROM or Listing 3 for 8K ROM.
Then trace through the program using
pencil and paper. You will see how the
unnecessary work is avoided.

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SYNC Program Listings

Readers should note the following
conventions used in the program listings
in this issue:

~ — The number symbol is used in
PRINT statements to show necessary
spaces.

"A, "— The underline is used in PRINT
statements to indicate graphics. Press the
ke\ designated in whatever way your
machine requires to get the graphic.

IN PIT - In PRINT statements when
a word or token is underlined enter the
word from the keyboard rather than type
it in letter by letter. This is a memory
saving technique.

After typing in a program line, you
must put the line into vour program. On
the ZX80and ZXK1 with *K ROM this is
done by hitting the NEWLINE key. On
the ZXM1 the same thing is done by hitting
ENTER. The words are used interchange
ably.

A number followed by a b is binary; a
number followed bv h is hex.

Line 55 initializes our new pointer to
one significant digit group. This is because
A(32), or rather, A(P), is the only digit
group with anything in it. Line 80 has
been changed to loop through only the
significant digit groups. You should verify
that this is correct.

Lines 143 through 147 have been added
to the carry processing section. They will
only be executed when there is a carry
out of a digit group. Line 143 checks to
see if this is a carry out of the currently
most significant digit group (the one P
points to). If not, this is simply a normal
carry, and carry processing is done.
Otherwise, lines 145 and 147 move the
pointer one digit group to the left and set
that digit group to 1 (the carry out of the
previous group).

With this modification in place, the
program takes just under three minutes,
an improvement of over 35 percent.

It should be apparent that you can use
this same technique to calculate other
"big" numbers. If you really want to
impress your friends, amaze yourself, and
give your ZX80/81 a workout, try calcu-
lating that wonderful constant, pi, to a
hundred places or so. You will have to
solve a few problems along the way, but
you have two months until the next issue
of SYNC comes in the mail... right?

By the way, in case you did not have
your ZX80/81 with you as you read this
column (perish the thought!), the answer
to our problem is (drum roll, please):
2, 707, 685, 248, 164, 858, 261, 307, 045,
101, 702, 230, 179, 137, 145, 581, 421, 695,
874, 189, 921, 465, 443, 966, 120, 903, 931,
272, 499, 975, 005, 961, 073, 806, 735, 733
604. 454, 495, 675, 614, 232, 576. jg

Llslins 1: 2 to tke 420tK (4K ROM).

10 DIM RC32)

20 FOR 1=1 TO 32

30 LET R (I) =0

40 NEXT I

50 LET R (32) =1

60 FOR N = l TO 4-20

70 LET C=0

80 FOR 1=1 TO 32

90 LET 11=33-1

100 LET fl(Il)=fl(Il)*£+C

110 LET C=0

120 IF Rill)<10000 THEN GOTO IS
3

130 LET R (ID =R f ID -1O000

14-0 LET C=l

150 NEXT I

150 NEXT N

17© FOR 1=1 TO 32

180 PRINT fltU .

190 NEXT I

Listins 2; Eliminating 0*2 (4K ROM). _

55 LET P=32

80 FOR 1=1 TO 32-P+l

14-3 IF NOT I1=P THEN GOTO 150

14-5 LET PsP-1

147 LET R <P> =1

Listing 3: Eliminating 0*2 (8K ROM). .

55 LET P=32

8© FOR 1=1 TO 32-P+l

143 IF IK >P THEN GOTO 150

145 LET P=P-1

147 LET ft IP) =1

DON'T JUST EXPAND YOUR MEMORY.
EXPAND YOUR HORIZONS.

Are you ready to put your ZX-81 to
work on some tough processing prob-
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16K/32K memory board with I/O
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Wisconsinc s I O ports consist of two
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With suitable external circuitry, they
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Even if you don t need the ports, you II
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SYNC Magazine

Finally

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ZXSl

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LEN
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The ZX81 is also very convenient to
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recall programs by name.
What you get. When
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get everything you need to
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It comes with connectors
for your TV and cassette
recorder, an AC adaptor, and
a free programming guide and
operating manual that corn-
Sinclair programs are available P letel Y documents the capabil-
ities of the ZX81.

Most people know by now that the
ZX81 from Sinclair Research is the
lowest priced personal computer in
the world.

But serious program-
mers are looking for more
than a low price. They're
looking for true computer
power. And that's where
the ZX81 surprises a lot
of people.

Just look at the key
board and you'll get
some idea of the
ZX81 's power. It
has more than 60
BASIC commands, 1
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A breakthrough in personal
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• Continuous display, including mo\ -
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• Multi-dimensional string and nu-
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• Mathematical and scienti-
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• Automatic syntax er-
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• Randomize function useful for both
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• Built-in interface for ZX Printer

• 1 K of memory expandable to 16K

• A comprehensive programming
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Options and add-ons. Like any
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Call toll free 800-543-3000. Ask
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call: 513-729-4300. Ask
for operator #509.
Phones open 24 hours
a day, 7 days a week.
Have your MasterCard
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These numbers are for
orders only. If you just want
Free guide to programming information, please
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2 Sinclair Plaza, Nashua, NH 03061.

To order call toll free: 800-543-3000.

AIL TO: Sinclair Research Ltd.,
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PRICE" QTY. AMOUNT

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inclair

Book Review

Understanding Your

ZX81 ROM Thomas L Keeney

Understanding Your ZX81 ROM by Dr.
Ian Logan. Melbourne House Ltd., Glebe
Cottage, Station Rd., Cheddington, Leigh-
ton Buzzard, Bedfordshire LU7 7NA, U.K.
162 pp.; paperback. Available directly
from the author for $18 (airmail). In U.S.
$19.95 from: Gladstone, Heuristics, Sin-
clair Place, Softsync.

SYNC readers will recognize Dr. Logan
as a major ZX80/81 expert whose writings
are well worthwhile. Understanding Your
ZX81 ROM is no exception. The book is
written for a serious beginner who has a
fairly good knowledge of Basic and wishes
to take advantage of Z80 machine code
execution speed. It supplements, but does
not replace, the ZX81 manual which must
be used as a reference. In many ways this
book is an extension of Dr. Logan's article
"An Introduction to Machine Code" in
SYNC 1:6.

The book falls logically into five parts.
The first is a brief review of the Z80
CPU, its registers, and its instruction
format. Next a quick introduction to the
internal arithmetic and number base
manipulations required is included.

Thomas L. Keeney, 9629 Dortmund, Huntsville
Al 35803.

The second part is a discussion of the
Z80 machine code instruction set grouped
by function. Examples are drawn liberally
from the 8K ROM. Dr. Logan includes 26
additional examples in the form of simple
Basic programs which can be entered and
executed in the IK memory.

A detailed examination of the relevant
parts of the 8K ROM makes up the third
part. The discussion is limited, however,
to those routines which the user can
reasonably access and use. Again, simple
Basic programs detail the manner in
which ROM based subroutines can be
applied to a program. A simple USR-
( address) will not work with most of them.
ROM functions for report generation,
character printing, keyboard input, and
display generation are discussed.

The fourth part might properly be
called "Getting Started in Machine
Code/' Dr. Logan introduces machine
code programming by treating it as an
extension to Basic. His technique of
writing Basic programs that mimic
machine code is unique to my experience.
This appears to be such a good teaching
method that it should become wide-
spread. Of course, the technique is possi-
ble only because the Sinclair Basic can

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accept variables of any length. Such
concepts as flowcharting and program
structure help get the beginner started.
Dr. Logan leads the programmer to think
in terms of the special needs of the CPU.
Finally, he discusses the integration of
the Basic and machine code into one
program. Demonstration programs illus-
trate the whole process.

The fifth part consists of appendixes.
Complete listings of the more important
8K ROM routines are given as well as the
usual tables of machine code language
instructions, decimal-hexadecimal conver-
sions, and keycodes.

Obviously, the book contains a great
deal of information, and you would pro-
bably want to keep it as a reference.
However, the book can be made easier to
use with three improvements.

First, the book clearly needs an index
and a revision of the physical arrangement
of some of the contents. For example, the
Z80 instructions set descriptions and the
8K ROM examples are separated from
the short programs illustrating their use.
This forces the reader to flip back and
forth between references. I spend a lot of
time with my fingers stuck in several
pages to keep track of the relevant subject
references while trying to apply the infor-
mation to a particular programming pro-
blem.

Second, since the 8K ROM is decimal
oriented, the inclusion of decimal equiva-
lents for the hexadecimal numbers would
remove some frustration for the beginner.
Granted that a book on machine language
needs some hex code information and
examples, but the extensive use of hexa-
decimal leads to some problems. For
example, the table of machine code
instructions in Appendix ii is useless as a
quick reference until the reader himself
enters the decimal equivalents.

Third, a more durable type of binding
that will allow the book to lie open and
flat so that the reader can use both hands
to enter program listings is needed. The
pages are starting to fall out of mine, and
I will soon ring bind it myself.

In spite of these three complaints, the
fact that I have worn out Dr. Logan's
book is an indication of how useful I have
found it to be. The fact that I intend to
repair it is an indication of how valuable I
think it will continue to be. It contains a
tremendous amount of information and is
well worth the cost. Understanding Your
ZX81 ROM would be a valuable addition
to most ZX80/81 libraries, and for the
serious programmer it should be high on
the list. PB

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Hardware Review

Sinclair ZX Spectrum

David Tebbutt

Well, he's done it again, hasn't he?
Uncle Clive has gone and shown the
world how to produce a decent colour
personal computer at the sort of price
only he can conceive. Two versions of
the Spectrum are available — 16k and
48k at £125 and £175 respectively,
including VAT. If you want to upgrade
your 16k machine to 48k later on, it
will cost you £60. At the moment, the
machines are available only by mail
order. The Spectrum (ZX Spectrum to
be precise) offers colour, high resolu-
tion graphics and sound and, at the

j^iat, it huo ju.ti fo VJ '" t,v * *-'*- MTO kswuu

value for money around.

Like most computers at this level,
the Spectrum plugs into the domestic
television and uses a normal cassette
recorder. The ZX printer can be
attached and, with a little modification,
ZX81 programs will run happily on the
Spectrum. A £50 miniature disk drive
(the ZX Microdrive), communications
facilities and an RS232 interface will be
announced later on.

Hardware

The Spectrum measures just 233x1 44x
30mm and weighs in at 520 grams
excluding the separate power supply
and cables. It looks extremely elegant
and, unlike its predecessors, it has keys
that actually press down.

You'll not be surprised to learn that
there are hardly any components inside
the machine: 14 chips, a UHF modula-
tor, a piezo-electric 'speaker' and an
assortment of capacitors, resistors,
diodes, crystals and a coil make up the
complement. I swear that some of my
crystal sets had more in them. All this
is mounted on a single board and,
looking underneath this production pro-
totype, I notice that there's not a single
patch. The only odd thing about it is
that there's a big blob of green plasti-
cine stuck around the coil. The coil on
the review machine does whistle a bit
but I understand that production
machines come with suitably lacquered
coils to eliminate this problem.

Reprinted with permission of Personal Computer
World, 14 Rathhone Place. London WIP IDE,
England.

A hefty edge connector at the back
brings out just about every signal you
could wish to have. This is used for
printers, communications and disk drive
connections. Inside there are two spare
sockets which accommodate each end
of the 32k memory expansion board.
This is a great improvement on the
ZX81 memory expansion which tended
to drop off the back of the machine at
the least provocation. Talking of sockets
(well I was, just now), every chip except
the ULA is socketed. The reason the
ULA isn't is because it gets darned hot
— putting it on the PCB allows the heat
to dissipate better.

The keyboard comprises a one-piece
grey rubber moulding mounted over a
pressure-sensitive membrane. The keys
poke up through holes in a black metal
plate and 1 must confess the feel is more
that of a calculator than a typewriter.
Most keytops have three symbols on
them and, in addition, most of them
have another two associated inscrip-
tions printed on the metal surround. If
you're anything like me you'll find
yourself reading the whole keyboard
each time you want to find a function.
You do get used to it after a while: in
my case it took a couple of days. I
found that red symbols on grey keytops
are quite difficult to read and, thinking
my eyesight might be going, I showed
the machine to a number of friends, all
of whom had the same difficulty. I
showed it to my 11 -year-old and he
thought it was just fine, though.

A power supply is included in the
price, so there's not a lot of point
risking one of your own and blowing
the Spectrum up. The two cassette leads
terminate in 3.5mm jack plugs so be
sure that they work with your recorder
before you embark on any major pro-
grams. It took me four or five tries
before I found the right volume setting
on my tape recorder. Once this was
found, though, program loading presen-
ted no problems.

1 tried the Spectrum on three tele-
visions and the results matched the
quality of the sets used. The display
comprises 24 lines of 32 characters with
the bottom two lines reserved for
messages and entries. The display can

also be regarded as 176 x 256 resolution
for graphics work. High resolution
graphics work is best done in two
colours as you will see in the Firmware
section of this review. The screen,
border and individual characters can
each take on one of eight colours and, in
addition to this, characters can be bright
or flashing. Other screen attributes
like inverse and overprinting relate to
the whole screen. More on these later.

The single channel BEEP facility
is about what you'd expect from a
piezo-electric speaker. It does sound
slightly better amplified from the
cassette port but it's still pretty awful.
A couple of octaves around middle
C aren't bad; but the other eight are
best used for sound effects. At the high
end they warble and at the low end they
grate — BEEP is a refreshingly honest
description.

Really, there's not a lot more to say
about the hardware. It is a very profes-
sional job; looks smart, works well and
manages to squeeze 191 legends Oii to
just 40 keys!

Firmware

Here's a new section for PCW Bench -
tests. All the software on the review
machine was in the ROM chip which
also contained the character set. This
time Sinclair has gone for a basic ASCII
set (upper and lower case) with the
addition of both built-in and user-
defined graphics characters. Outside of
the range SPACE to QUOTES (32 to
126), many of the codes have special
values relating to Spectrum keys and
functions. For example, you'll find a
copyright symbol key. (Now why didn't
anyone else think of that?) You can
define up to 21 characters of your own.
Two screen tables are maintained in
memory — one for the displayed charac-
ters themselves and the other for the
attributes which describe how they're
to be displayed. These attributes can be
tested from within a Basic program. The
character colour is referred to as INK
while the background colour is called
PAPER. Isn't that sensible? Each
character can have its own value for
INK, PAPER, FLASHING, BRIGHT-
NESS, INVERSE and OVER. The last
two should be explained: INVERSE
simply means that the dots which form
the character are printed in the PAPER
colour while the PAPER is printed in
the INK colour. OVER is special: it
allows you to merge a new character
with the one already at the screen posi-
tion. The rules are that two INKs or two
PAPERs print PAPER otherwise it
prints INK. This means that you have a
neat way of removing the last thing

SYNC Magazine

printed and restoring what was there
before it.

By now you have probably realised
why it is best to stick to two colours
when doing graphics work. Since the
colour of the INK and PAPER relates to
a whole character position, then each
time a new colour graphics point is set,
all other set points within the boundary
of that character are set to the new
colour. This makes for a very curious
effect to say the least.

Mathematical accuracy is to 94
decimal digits and a fairly full range of
mathematical functions is accessible
from the keyboard. While on the sub-
ject of keyboards, this one has a built-in
software 'click 1 , an upper -case lock key
and automatically repeating keys. Like
the ZX80 and ZX81 before it, the
Spectrum makes great use of single
stroke keyword entries. In fact, I think
every standard function and command
is obtainable in this way. You'll even
find things like >= and <= occupying
their own pieces of grey rubber.

Basic

The Spectrum comes with a very useful
version of Basic. It will be quite familiar
to anyone who is used to the Micro so ft
types of Basic and a doddle to learn for
those new to the language.

Rather than go through all the
features and functions of the language,
I have summarised them in a separate

box. Here, I'll just comment on the
unusual and interesting aspects of this
particular implementation. Unlike some
Basics, it is a teeny bit strict about
things like using LET before assigning a
value to a variable name or putting
GOTO after a THEN. My view is that
this is all jolly good discipline and it
is more than compensated for by the
fact that Spectrum pops in all those
spaces which make programs so much
easier to read. Of course, once you've
found your way round the keyboard,
the single stroke keyword entry is a
joy. (I've got a feeling I said that in my
last two ZX reviews.)

SAVEing and LOADing cassette
tapes gives plenty of scope on this
machine. You can save a program nor-
mally, you can save it so that execution
starts automatically when it is reloaded,
you can save arrays, you can save parti-
cular chunks of memory and if you
want to keep a pretty picture you've
created then you can use the SCREEN?
option to save that too. All saved pro-
grams can be verified after saving. The
screen save can't be verified because the
display is changed during the verify
program and it would not then match
that held on tape. The LOAD command
can, of course, handle any tape created
by SAVE. The MERGE command
allows you to merge a program on tape
with one already in memory. Program
lines which are duplicated are over-

written while all others are suitably
interleaved.

The graphics facilities are great fun.
You can draw straight lines, curves and
circles on the 176x256 pixel (Picture
ELement, or dot) window. Position 0,0
is at the bottom left-hand corner of the
screen. You can define up to 21
graphics characters of your own which
is a superb feature if you're into writing
your own Space Invader or Pack -Man
games. I had a lot of fun drawing and
animating little people on the screen.
The nice thing is that you can do all
this sort of thing without leaving
Basic. A BIN (binary) notation has been
introduced which allows you to define
numbers as a series of 0s and Is — just
the ticket for designing funny charac-
ters. Each character comprises eight
lines of eight points, so a succession of
eight BIN numbers is all you need to
define such a character. Another use for
user-defined graphics is to squeeze some
extra colours out of the machine. If you
lay out the 64 pixels like a chess board
and choose suitable INK and PAPER
colours then you can get some interest-
ing effects. Most of them will be awful
but persevere — some will be good.

You won't be surprised to learn that
line drawing and circle plotting are
achieved using the DRAW and CIRCLE
commands. A PLOT command allows
you to plot single points. POINT
enables you to find out whether a parti-

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SYNC Magazine

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cular pixel is set. You always DRAW
from where Spectrum thinks you are on
the screen. For example, a command
DRAW 10,10,pi would draw a semi-
circle ending up 10 places to the right
and 10 above the current position. A
fraction of pi would provide a different
arc while zero, or no third argument
(DRAW 10, 10) would draw a straight
line. The curve can be drawn on either
side of the centre line by making
the third argument a positive or nega-
tive number.

The CIRCLE command uses three
arguments: x-axis, y-axis and radius.

Remember, the OVER command can be
used to erase something already drawn.
I used this feature in conjunction with
DRAW, PLOT and CIRCLE to create
cartoon effects. OVER is also useful for
embedding text in a drawing. When set
on, the text merges with the existing
lines in the drawing. When set off it
prints the full 8x8 character, completely
replacing anything already displayed at
that position. Incidentally, SCREEN?
can be used to return details of the
contents of a character position. Used in
conjunction with the PRINT AT
command, this could be a good way of

Spectrum Basic

Functions

ABS ACS

AND

ASN ATN

ATTR

BIN CHRS

CODE

COS EXP

IN INKEYS INT

LEN LN

NOT

OR PEEK PI

POINT RND

SCREENS

SGN SIN

SQR

STR$ TAN

USR

VAL VALS

Operations

+ -*=><

Statements

BEEP

DATA

GO TO

LOAD. .DATA

OVER

RETURN

BORDER

DEF FN

IF. .THEN

LOAD. .CODE

PAPER

RUN

BRIGHT

DELETE

INK

LOAD. .SCREENS PAUSE

SAVE

CAT

DIM

INPUT

LPRINT

PLOT

SAVE. .LINE

CIRCLE

DRAW

INVERSE

MERGE

POKE

SAVE. .DATA

CLEAR

ERASE

LET

MOVE

SAVE. .CODE

FLASH

LIST

NEW

RANDOMIZE

SAVE. .SCREEN?

CLS

FOR. .TO.

.STEP

READ

STOP

CONTINUE

FORMAT

LLIST

OPEN #

REM

VERIFY

COPY

GOSUB

LOAD

OUT

RESTORE

making your program find a suitable
place to print a sort of 'label' on a draw-
ing. The AT allows you to define the
row and column at which printing
should start.

A few instructions I particularly
noticed as I went though the manual
were READ, DATA, RESTORE and
VAL$. READ and DATA are old
friends although I can't remember
them being on previous ZX machines.
Using the DATA command you can pro-
vide lists of information at the begin-
ning of a program. Each READ instruc-
tion takes the next word from this list.
RESTORE can be used to set the DATA
pointer to any DATA statement. VAL?
baffles me — it strips the outside quotes
from string expressions and returns the
string value of the result. Perhaps some
kind reader would care to suggest a
worthwhile application for this feature.

Now let's have a look at our honestly
named friend, BEEP. There's not a lot
to tell, really, except that you can
control both pitch and duration. Notes
below middle C are represented by nega-
tive numbers, those above by positive.
Twelve numbers make an octave. (If
you look at a piano keyboard you'll
find that there are seven white notes
and five black notes per octave.) Middle
C is zero. The duration is expressed in
seconds or fractions of a second. As I
mentioned earlier, the sound isn't,
brilliant but it has the saving grace of

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LEFTSCROLL S

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The Sinclair ZX81 basic course 35.00

Cassette Tapes

ZX Chess - 16K ZX80^K7ZX81 24.50

10 Exciting Programs- IK ZX81 14.95

Adventure A - 16K ZX80-8K/XZ81 19.50

Adventure B - 16K ZX80^8K/ZX81 19.50

Adventure C - 16K ZX80^8KyZX81 19.50

Spacetrek — 16K ZX81 14.95

Directory/Record— IK ZX80-8K/ZX81 14.95
with listing

Reversi— IK ZX80^8K/ZX81 14.95

Super Invasion - IK ZX80^8K/ZX81 14.95

Wallbusters- IK ZX80-8K/ZX81 14.95

ZX Galaxians - 16K ZX81 14.95

ZX Bug Utility Program -16K ZX81 2430

If you are a producer of quality hardware or
software for Sinclair products and are interested
in having a U.S. or Westcoast organization
marketing your products we would like to hear
from you.

NO HANDLING OR SHIPPING CHARGES
Washington residents add 6.5% sales tax.

P.O. Box 2288, Redmond, Washington 98052

being fairly quiet (ComputerTowns
please note). You can pick this sound
up from the cassette ports if you so
wish. I'd say these facilities are more
likely to be used for sound effects than
composing symphines.

That's really all I have to say about
the Basic. It is a very good implementa-
tion for a machine of this size. A
PAINT instruction would have been
nice to fill in graphics shapes, but I
think it would look a bit weird in multi-
colour mode with the colours changing
at each character boundary. A routine
to do this should be simple enough. I
think the screen resolution is quite ade-
quate for most personal users of the
machine. In fact you can churn out
some quite stunning effects using
DRAW, PLOT, CIRCLE and the user-
defined characters.

Before moving on to documentation,
here's a list of the disk commands just
to whet your appetite: CAT, CLOSE,
DELETE, ERASE, FORMAT, MOVE,
OPEN. CAT is probably short for
Catalogue which lists the files on a disk.
MOVE probably copies a file from one
place to another. The others are self-
exaplanatory.

Documentation

Two manuals come with the Spectrum
— a thin but useful introduction for the
complete novice and a thicker one
which explains things in depth. A lot
of effort has been put into this latter
manual. It is professionally presented
and easy to read. Unfortunately, I was
given a photocopy of the final proofs
and it contained no index and no table
of contents. I read the whole manual a
couple of times before starting the
review and I found it a real problem to
find things that I knew were there
somewhere. I must admit that the style
wasn't to my liking; it's a little verbose
and the individual chapters seem to lack
structure. I also found the inevitable
errors which might cause a beginner

What about the 81 ?

It was no secret that * Uncle' Give
was going to launch a knockout micro
— he's put a bomb under the industry
twice already, producing machines
which brought computing power with-
in everybody's reach at prices which
drastically undercut the competition.

A slightly upmarket (by Sinclair
standards) machine offering colour
and sound and reasonable graphics at
a price far, far below that of any
equivalent machine was a logical step
to take, especially in view of Sinclair's
obvious annoyance at being left out of
the BBC deal.

What is interesting, though, is that
the Spectrum does not replace the
ZX81, as the 81 did the 80 - it's an
addition to the range and the ZX81
will continue in production. In fact,
production of the 81 is to be increa-
sed to a target of 150,000 a month by
the end of the year.

The ZX81 will continue to be ideal
for the person who wants the lowest
possible entry cost into computing,'
says Sinclair. And to prove the point,
he's knocked £20 off the price of the
16k RAM pack.

At the moment Spectrum is avail-
able only by mail order and is only
on sale in the UK — there are no plans
yet to market it through retail outlets,
as is done with the ZX81 through
W H Smith, and export versions are
not planned until the end of the year,
with the USA being the first (and
largest) market to get the new
machine.
Peter Rodwell

problems — things like a minus sign
being printed instead of equals, for
example. The manual certainly seems
to cover everything, so if a table of
contents and a comprehensive index are
added you'll probably find it adequate.
It's certainly an improvement on many
manuals on the market.

Potential use

This is the first machine that I've
reviewed since the Atari two summers
ago that I would actually buy — in fact
I will have probably ordered one by the
time you read this. I would use it for

fun, for fooling around with graphics
and for programming in Z80 code. I
would treat it as a hobby machine, a
way of relaxing. My children have
already become very interested in the
graphics capability and I see this as a
way of giving them a real understanding
of mathematics. A Logo system on this
at the right price would go down an
absolute treat — if anyone out there
thinks of doing it, I'd love to review it.
Of course, there are those who want
to learn to write programs. Once again,
this is an excellent machine to cut your
teeth on. I think that schools and

ZX 80/81
1 6K RAM

Plug in and Run-

This RAM Memory Expansion
has a reliable, proven connector
and requires no additional power
other than that supplied by
the ZX 80/81.

Fully tested with a 90 day warranty

Apropos tcchnoiogi

To Order:

Send Check or M.O.

$45.95 + $4.00 S & H

or Phone: 805/482-3604

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Cal. Residents Add 6% Sales Tax.

350 N. Lantana Ave., Suite 821 • Camanllo, CA 9301

SYNC Magazine

homes have got to be the prime targets
for Spectrum at the moment.

Later on when the disk drives appear,
this may change. At a predicted £50 for
a 100k drive, a lot of people who will
have written the Spectrum off as a
hobby machine will have to think again.
Add to that a £20 combined KS232
and communications facility, and you
could be talking about some very
interesting and fairly sophisticated net-
works. At that stage, it becomes a very
real prospect for schools looking for a
fairly grown-up system, but one which
can involve as many pupils as possible.
At Sinclair's prices could we possibly
be heading for the 'one on every desk'
scenario painted by so many futurolo-
gists?

Until those disks arrive there is no
great office potential for the Spectrum.
Once they're on stream then it's pro-
bably just a question of appropriate
software. Information management and
Visicalc-type applications would seem
to be the most likely and, because of
the price of the television, they will
probably be used with portable black
and white machines. No doubt the
dedicated will take their Spectrums (or
is it Spectri?) home to plug into the
colour TV. Most people will probably
wait until Sinclair announces a flat
screen colour television. The network
idea could then be useful in offices for
things like telephone directories, notice-
boards and memos.

Prices (inc VAT)
16k Spectrum
48k Spectrum
32k Memory
Microdrive disk
RS232 + Comms
ZX Printer

£125

£175

£60

(estimated) £50

(estimated) £20

£59.95

Conclusions

Well, for the benefit of those who only
read the first and last paragraphs of
these reviews here are my conclusions:
Clive Sinclair has produced a very good
16k personal computer which offers
colour, high resolution graphics and
limited sound for just £125. That
represents very good value for
money provided that this is the sort of
machine you want. It is ideal for people
who want to learn about computing and
have a lot of fun while they're doing it.
Given the right sort of graphics-based
educational software, it can bring
people very pleasurable ways of learning
subjects such as mathematics and
geography. Once the games programs
start to appear, a lot of people will use
it just for that, although it does seem a
bit of a waste.

Later on, the provision of disk drives
and communications facilities will make
it an even more serious contender for
the school markets and it will begin to
creep into businesses. When the flat
screen television appears then I suspect
that the business interest will rise
because the price will be far more
appropriate. Bulletin boards, memos,
telephone directories, spreadsheet cal-
culation and information management
seem to be the most likely applications

The 'proper' keyboard is "a distinct
improvement on its predecessors, but it
still doesn't achieve — or try to achieve
— the quality of an IBM. All the old
regular Sinclair features are included —
the single keyword entry and the auto-
matic syntax checking as you enter each
command, for example.

My verdict? The best value for
money you can find today! %

/ would like to thank John Mathieson
of Sinclair Research for so patiently
answering my questions.

BM1
BM2

4.8
8.7

BM3
BM4

_ Benchmark timings .

21.1 BM5

20.4

BM6

24.0
55.3

BM7
BM8

80.7
25.3

All timings in seconds.

.Technical data .

CPU: 3.5MHzZ80A

Memory: 16k Dynamic RAM, 16k ROM, 32k expansion option

Keyboard: 40 keys rubber moulding. 183 functions + 8 colour labels.

Auto -repeat

Screen: Domestic colour television. 8 Colours or 6 grey shades.

Cassette: Domestic recorder.

Disk drives: To be announced. 100k per drive.

Ports: To be announced. RS232 & comms.

Language: Basic in ROM

Sin ware's

HOT Z

HOT Z is a program designed to give you
the control and understanding of your
computer's soft side that you will need to
get the most out of the new generation of
ZX equipment. Use it to manage the con-
tents of that 64K memory or to write I/O
routines for peripherals. Use it to under-
stand your ROM and get the best out of
your hardware, or to learn machine pro-
gramming, which is much less forbidding
when you have the power of HOT Z's 40
commands at your fingertips.

HOT Z provides:

• Disassembly of Z80 code, floating-
point code, CHR$ code, with named
system variables and no warmed-
over 8080 jingo.

• The ability to annotate your memory
with hundreds or thousands of labels
for better understanding of programs
and files. Full set of HOT Z labels
supplied.

• Easy cursor-guided entry of machine
programs with instant disassembly of
each step.

• Edit functions to insert, delete, trans-
fer, clear, search, load or save blocks
of memory.

• Single or multi-stepping of programs
anywhere in memory, even ROM or
above 32K, with full display of regist-
ers and flags.

• Smooth fast 24-line displays at all
times.

• Instant access to command prompt
displays.

• 50 pages of instruction and docu-
mentation.

• An expandible system: Assembler
available soon.

HOT Z shares memory space with BASIC
programs, is stable, friendly, and re-
freshes the flip-flops that other programs
cannot reach. Special versions for 16K
RAM, 32K+ RAM, ZX80 or 81. Specify.
$19.95 ppd.

SINWARE

BOX 323, DIXON, NM 87527

July/August 1982

8K ROM; IK RAM

Double Your Memory

J. Wayne Schneider

Ed. -A WORD OF CAUTION: Any

hardware project for your computer must
be approached with extreme caution.
SYNC cannot he responsible for any
problem that may arise from attempting
hardware projects. Obviously, any dam-
age to your computer can be costly in
time and money.

The first few days of working (playing?)
with a new Sinclair ZX81 are filled with
anticipation, excitement, and, for the kit
builder, triumph and pride. Seeing that
little black K on the screen when the
ZX81 is first powered up brings exclama-
tions of joy from the new programmer
and a questioning stare from uninitiated
bystanders. Alas, all of this excitement
soon dwindles into frustration with the
first attempt to impress a sceptic viewer
with a simple random graphics display.
There is not enough RAM for even one
full screen and a modest program.

Do not despair! There is a reasonably
quick and almost painless solution.
Although the ZX81 was designed to be
inexpensive, a foresighted designer has
provided the circuitry to use a 2K x 8 bit
static RAM on the circuit board. The
whole process involves removing the two
21 14s at IC4a and IC4b, installing a 2K x
8 RAM at IC4, and adding a jumper at
L2. If you are lucky enough to have a
ZX81 with a 4118 RAM, you will not
even have to change IC sockets. Simply
remove the 4118, install the 4802 in its
place, and change the jumper at LI to L2.
One warning for those with factory built
computers: performing the procedure
described here will void your warranty.

J. Wayne Schneider. 1601 South 450 West, Prove,
UT 84601.

Preparations

You will need a clean, dry workspace
at least two by four feet. The area should
be well-lighted and protected from solder
drippings. An old bath towel spread over
a table makes an excellent surface on
which to work, but make sure it is an
expendable towei before you burn a hole
in it with a hot soldering iron. Further-
more, it protects both the table and the
ZX81.

You will also need the following:

1) A light, 15-25 watt soldering iron
with a fine tip.

2) Fine gauge rosin core solder.

3) A pair of sharp wire cutters.

4) A Phillips screwdriver with a no. 1
point.

5) A 2K x 8 static RAM. These are
manufactured by several companies.
Mostek's 4802 is no longer being manu-
factured, but it is still available from many
electronics supply stores. Mitsubishi
makes an equivalent part that costs less,
number M58725P. Hitachi's CMOS part,
number 6116, which requires considerably
less power, is your best bet if you are
concerned about the ZX81 overheating.
Others are the Toshiba 2016, the Fujitsu
MB8128, and the NEC part 4016.

If your ZX81 has the two ICs labeled
uPD2114LC, you will need to buy a 24
pin DIP socket for the new RAM or else
two 12 pin SIP sockets. The DIP (dual
inline pin), socket is structurally better,
but the SIPs can be installed without
removing the old 18 pin socket. You will
need some solder wick to help with the
desoldering of the old 18 pin DIP socket
if you are going to add a 24 pin DIP
socket.

New rubber feet or glue will be needed
when you reattach the rubber feet to the
back cover of the ZX81.

When you have all of the parts and
about three hours to spare, you are ready
to begin.

Operations

Get all of the parts and tools together.
Disconnect the ZX81 from everything,
especially from the power supply. Place
it flat in front of you just as though you
were going to type on it.

1) Remove the back cover.

Turn the ZX81 over so that it is posi-
tioned as shown in Figure 1. There are
five screws to remove. Only two of them
are visible. The other three are under the
rubber feet at positions 1, 4, and 5,
Carefully remove the three rubber feet
and save them for later. If you are lucky,
the sticky will come with them, and they
can be stuck to a piece of wax paper for
installation later. Now remove all five
screws. Notice that screws 4 and 5 are
shorter. Set these in a safe place. Gently
lift or pry the back cover off. It should
come easily without forcing.

2) Remove the printed circuit board.
Remove the two screws that hold the

printed circuit board in place. Note their
exact position for reassembly. Very care-
fully lift the circuit board and rotate it
back towards you until it is face up. Be
extra careful not to stress or crimp the
flat tails connected to the keyboard. You
may now disconnect the keyboard by
pulling straight and steady on one tail at a
time. Set aside the cover with the key-
board attached.

3) Remove the existing IK RAM.
Turn the keyboard around 180 degrees

so that the flat square metal heat sink is
on the lower left as shown in Figure 2,
Remove the two 18 pin ICs at IC4a and
IC4b. These are the 2114 IK x 4 bit
RAMs. If your ZX81 does not have these
two ICs, then it will have only one 24 pin
IC at IC4. Remove this IC. It is a 41 18 IK
x 8 bit RAM. Save the RAM where it will
not be subject to extreme temperatures
or static.

4) Install the new IC sockets.

If you are one of the lucky ones whose
ZX81 came with a 4118 RAM, you can
ignore this process. Otherwise, carry on.
Place the new sockets in the lower 12
holes on each side of location IC4. If the
SIPs do not fit easily into the holes or if
you are using a DIP socket, you will have
to desolder and remove the 18 pin DIP
socket. Now turn the board over and
solder the new socket in place. (Caution:
never bring a hot soldering iron close to a
chip or any other component. Be sure
that all the chips have been removed.) Be
careful with the solder. Use enough to fill
the hole but not so much that it runs
down the pins and shorts something out.
Turn the board back over.

SYNC Magazine

.Figure 1: Bottom of the ZX81.

Figure 2: Board Orientation and IC Location.

Long screws

Short screws

-> @

5) Install a jumper at L2.

Those who have the 4118 RAM must
first desolder the jumper at LI. Use a
short piece of wire bent in a U shape to
connect the solder pads at L2. Solder it in
place. Be careful not to get too much
solder.

6) Install the new 2K RAM IC.

Place the new 2K RAM in the new
socket. It should be oriented with pin 1 to
the upper left. Finding pin 1 may be a
problem. The IC will probably have a dot
etched or molded into the top surface
adjacent to pin 1. If you cannot find a
dot, there will be a notch in the center of
one end. The notch should face away
from you. If you had a 4118 RAM. be
sure you are installing into the lower 24
holes. Nothing goes into the upper four
holes. Push the socket into place. You
may find it necessary to bend the pins
inward to make it fit. After the IC is in
place, inspect it to be sure that all the
pins are in their holes and not bent
underneath the IC.

7/ Reassemble the ZX8L

Turn the printed circuit board 180
degrees so that the square metal heat
sink is at the upper right. Place the cover

beneath the circuit board. The keyboard
tails should form a graceful loop back
over the upper left corner and into their
sockets. Be very careful when pushing
these fragile tails into the sockets. If they
are bent or torn, you will not have much
success in getting the ZX81 to work.
Rotate the circuit board back into place
in the cover. Check the keyboard tails for
positon. Screw the board in place with
two of the short screws at the positions
you noted in step 2. Replace the cover
and screw it down using the short screws
at locations 4 and 5. Do not use the long
screws in the wrong place. You could
damage the keyboard. Glue the rubber
feet into place. When you install the
rubber feet, place them to the side of the
screw holes, and you will never have to
go through that misery again.

Trouble

Connect your ZX81 to your TV again
and plug in the power. If it works, treat
yourself. If not, check the solder joints.
You may have to resolder them. Do not
resolder with the IC in the socket. Check
the IC for orientation. Be sure all of the
pins are in the holes. Did you forget the

jumper? If the computer displays the
inverse K but will not respond to the
keyboard, check the tails. They should
be seated straight in their sockets. The
fault rarely lies within the RAM IC itself.
However, that is a possibility. At that
point you will need someone experienced
in working with digital circuits to help
you solve the problem.

Conclusion

Now that you are up and running, try
the following command:

PRINT PEEK 16389*256-16384
That should display 2048, which is the
amount of memory you now have avail-
able. A full screen requires 704 bytes of
memory The system variables require 125
bytes. With IK of RAM, you are left with
195 bytes for a program. With 2K of RAM
you are left with 1219 bytes; over six
times as much program space. Of course,
the ZX81 Basic does not really dedicate
704 bytes of memory unless your program
fills the thirty-second position of every
line. That will rarely happen, but now
you can enter a reasonably long program
and still have a full screen display if you
want it. *m

July/August 1982

ZX81

SOFTWARE

DAMES PACKS

I for 1K ZX81 & 8K ROM ZX80. Eight
fantastic programs for the
unexpanded ZX81, including
DIGICLOCK, 9-LIVES, REACTION TEST,
GOBBLER and PATTERNS.
$9.95 ($12.95 in Canada)

2 for 16K ZX81. Four programs writ-
ten in BASIC for the expanded
ZX81. PONTOON, FRUIT
MACHINE, OXO, and BIO- RHYTHMS.
$9.95 ($12.95 in Canada)

J for 16K ZX81 and 8K ROM ZX80.
Two programs for expanded ZX81
to keep you entertained for hours!
3-D 0X0 is written in machine code and is
hard to beat. MARS RESCUE is a com-
pulsive adventure game.
$9,95 ($12.95 in Canada)

4 for 16K ZX81. ZOMBIES — escape
as they chase you around Zombie
Island. Lure them into the pits, but
don't fall in yourself. MOUNT MAYHEM —
can you reach the 20,000 foot summit?
Look out for Yeiis and other hazards!
$9.95 ($12.95 in Canada)

DICTATOR

Fantastic new adventure game for 16K (or
greater) ZX81. You have just become 129th
ruler of Ritimba with a single goal in mind:
take full advantage of the situation for
your own good. You have to deal with a
handful of factions: unruly army,
downtrodden peasants — but you have
the secret police on your side.

$14.95 ($17.95 in Canada)

CONSTELLATION

Turn your ZX81 into a telescope with this
amazing 16K program. Produces a simula-
tion of the night sky as seen from any
position on Earth at any chosen time this
century. You may point your telescope in
any direction, move it up, down, left or
right, zoom in or out. Stars may be
displayed by magnitude or constellation
$14.95 ($19.95 in Canada)

CHESS

A challenging chess programme, written
in machine language, designed to operate
in the ZX81 fast mode. ZX Chess allows
you to select from 6 levels of play, choose
either black or white, and enables castling
and en passant moves. Unique "self-
running" feature: you start the tape and
when the chess board appears on the
screen, start your game.
ZX CHESS! N ow $12.95

On
Cassette

IXAS

Assembler

Now you can use the full power of the Z80
microprocessor without having to
laboriously POKE in instruction codes.
This full specification Z80 assembler
assembles all the standard Zilog
mnemonics, which are simply written into
REM statements (more than one per line is
allowed) within your BASIC program.
When assembled, the assembly listings,
together with assembled codes and
adresses, are displayed on the screen.
The assembled code is executed by USR.
The program occupies 5K, is situated at
the top of the memory, and is protected
from overwriting. This means that ZXAS
may be used in conjunction with ZXDB
(see below), providing an extremely power-
ful machine code system normally only
found on very expensive computers.
The program is available for both the ZX81
and the 8K ROM ZX80, and in both cases,
the 16K RAM pack is required. Despite the
low price, ZXAS is a FULL-
SPECIFICATION assembler, and is a must
for all serious ZX users. Full documenta-
tion on how to use the assembler (in-
cluding a list of the mnemonics) is sup-
plied.
$9.95 ($12.95 in Canada)

VVJID Disassembler/

minrnJU Debugger

The perfect complement to the ZXAS
assembler, ZXDB is a complete combined
machine code disassembler and debugg-
ing program. Like ZXAS, it is itself written
in machine code for compactness, and
may be used in conjunction with ZXAS,
still leaving about 9K of memory for your
own program.

Apart from the DIASSEMBLER, the pro-
gram has features including SINGLE
STEP, BLOCK SEARCH, TRANSFER AND
FILL, HEX LOADER, REGISTER DISPLAY
and more, all of which are executed by
simple one key commands from the
keyboard. All in all, an extremely powerful
programming aid, well worth the money
for the disassembler alone!
$9.95 ($12.95 in Canada)

STAR TREK

The classic computer game in which you
trek across the galaxy in search of Kl-
ingons to zap with your phasers and
photon torpedoes. You have long and
short range scanners to help you find
them, Starbases to refuel your ship at and,
of course, various witty comments from
the crew. 16K.
$9.95 ($12.95 in Canada)

VU-CALC

VU-CALC. Constructs, generates, and
calculates large tables for analysis,
budget sheets and projections. Up to 26
columns of figures or data can be entered,
plus user definable formulae capable of
relating any one or more position in the
table to any other defined position.

NOW $14.95

MULTIFILl

cc> i^ai t3uG-e>-rE

*FT UP FILE PflRHMETERS

CREATE F ILE

MODIFY FILE

SERRCH FOR FILE

STEP THROUGH FILES

SUH NUMERICAL FILE

SECURITY LOCK

SPUE FILES ON TAPE

ENTER YOUR CHOICE

MULTIFILE

Data Storage System

An amazingly versatile multi-purpose fil-
ing system for the 16K ZX81. The program
is menu-driven, and number, size and
headings of files are user-definable. Both
string and numerical files are catered for.
Files may be created, modified, replaced,
and searched, and are protected by an in-
genious foolproof security system. Out-
put to the ZX printer is also provided. The
program comes on cassette, together with
three quality data cassettes for file
storage, and comprehensive documenta-
tion, describing a host of applications for
both business and personal use. Supplied
in an attractive storage case. If your ZX81
is bored with playing games, then this pro-
gram will give it plenty to think about!
$29.95 ($39.95 in Canada)

New Multifile Plus for 64 K RAM $34.95

VIEWTEXT

A ten page information display system for

the 16K ZX81. Can display both text and

graphics in any sequence with variable

speed. Many applications including shop

window displays, educations, animation,

etc

$14.95 ($17.95 in Canada)

Gladstone Electronics, 901 Furhmann Blvd., Buffalo, N.Y. 14203 (716) 849-0735

ZX81 COMPLETE
BASIC COURSE

At last, a comprehensive text lor your Sinclair ZX 81 !
The complete BASIC Course is a manual which will
immediately become an indispensible work of
reference tor all your ZX 81 programming

Whether you have never done any programming or
whether you are an experienced microcomputer
user, the Complete BASIC Course will provide itself
to you as an invaluable aid

The Complete BASIC Course is designed to teach
you to write and develop BASIC programs for the
Sinclair ZX 81 - no other books or aids are
necessary All is revealed in our easy step-by-step
guide with programs and test yourself exercises all
the way through

As you become more proficient with computing, the
Complete BASIC Course will continue to be an
essential guide, giving you finger tip references,
numerous advanced programming techniques and
memory saving devices specifically for the Sinclair
ZX81

HOW TO WRITE PROGRAMS:

Even it the idea of writing programs is completely
mystifying to you, the Complete BASIC Course will
show you just how easy it is In no time you will be
able *c writs and snjoy ccmp'e* programs for
whatever use you desire.

Using the proven TOP-DOWN approach, the
Complete BASIC Course will show you systematic
and simple ways to write programs. Even
experienced programmers will benefit from this
Course, making programs easier to write and less
prone to error 1

NUMEROUS EXAMPLES:
Every concept, every function n fully described by
simple programs that you can enter on your Sinclair
ZX61 In minuter

MORE BOOKS!

Not Only 30 Programs (or the Sinclair ZX81: 1K-

Not only over 30 programs, from arcade games to the
final challenging Draughts playing program, which all
fit into the unexpahded 1K Sinclair ZX81 but also
notes on how these programs were written and
special tips! Great value!
$14.95 ($16.95 in Canada)

Machine Language Programming Made Simple lor the
Sinclair

A complete beginner's guide to the computer's own
language Z80 machine language Machine language
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Discovering the ROM
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Part 3

Understanding Floating-Point

Arithmetic Ian S. Logan

In this article on floating-point arith-
metic we will consider the algorithms that
are used in the 8K ROM program to
perform the operations of subtraction,
addition, multiplication, and division. The
8K ROM program has four separate
subroutines for performing these arith-
metic operations. The hex addresses of
their entry points in the 8K ROM
(improved) are:

Subtraction: 174C
Addition: 1755
Multiplication: 17C6
Division: 1882

In each case the subroutine performs
its operation on the top two floating-point
numbers found on the "calculator stack,"
and returns the result as a single floating-
point number that replaces the "lower" of
the two operands. The pointer to the end
of the calculator stack (STKEND) will
point five locations lower after each
operation in consequence.

Now, before going into the details of
these four subroutines, let me recap how
a floating-point representation of a deci-
mal number is produced.

In the ZX80/81 system floating-point
numbers occupy five bytes. The exponent
takes one byte, and the mantissa, four.

The first stage, therefore, is to consider
your decimal number in E format. It is a
convention that the mantissa has only a
fractional part and thereby starts with a
decimal point. To illustrate the process
let us take the number 456.

The decimal exponent will be +3, and
the decimal mantissa will be .456. Note
that the number is positive.

Next the operations should be repeated
in binary to obtain a "true" binary floating
point. The binary representation of 456 is
1 1100 1000. The exponent is +9 or 1001
and the mantissa will be 1 1 10 0100

Dr. Ian S. Logan, 24. Nurses Lane, SkeHin«thorpe
Line Ion. LN6 OTT. U.K.

Now the exponent and mantissa can be
made up to the correct size and expressed
in hex as follows:

Exponent: 09 (1 byte)
Mantissa: E4 00 00 00 (4 bytes)
To obtain the correct Sinclair repre-
sentation there are two further conven-
tions to follow:

1) Add 128d (80h) to the exponent.

2) Replace the first bit of the mantissa —
it is always set!— with a zero if the number
is positive.

Hence, the final representation for 456
will be:

89 64 00 00 00 in hex, or
137, 100, 0, 0, in decimal.
Now let us consider the actual sub-
routines.

Subtraction

The subroutine that is uniquely used
for the operation of subtraction is very
short as the algorithm used is to change
the sign of the subtrahend (the number
being subtracted) and then to proceed
with an addition. The actual steps are:

1) Fetch the subtrahend and return if it
has the value 0; i.e., 456 - is always 456
and the operation of subtracting a zero
can be ignored in all cases.

2) Fetch the first byte of the mantissa
of the subtrahend and "flip" the sign
bit-the first bit: 456-315 = 456 + (-315).

3) Proceed to add the two numbers.

Addition

This subroutine is fairly complicated as
it has to cater for simple additions of
positive numbers whose results are
"within range," for additions with negative
numbers, and for additions that go "out
of range."

The essential parts of the subroutine
are, however, fairly easy to explain. The
steps are:

1) Fetch the augend (the first number
of the addition). Reduce the exponent by

July/August 1982

80h, restore bit 1 of the mantissa if the
number is positive and make a note of the
sign of the number. The augend is now in
a "true" floating-point form.

2) Fetch the addend (the second num-
ber of the addition) and produce its "true"
floating point form.

3) Compare the "true" exponents
against each other and, if the addend is
larger than the augend, switch over the
numbers. I.e., when adding 456 + 38, the
exponents in decimal are +3 and +2, so
leave as is. But, when adding 38 + 456,
switch over the numbers to make 456 +
38.

4) Find the "difference" between the
exponents. This difference is the "amount
of shift" that will be needed to "line up"
the addend for the actual addition. This
can be shown in decimal as follows:

456 + 38 is (.456 E + 3) + (.38 E + 2)
The difference in the exponents is +1,
and the addend is shifted one place to the
right to make the addition:

(.456 E + 3) + (.038 E 4- 3)
Now the true addition takes place
between the mantissas, and the result is
(.456 + .038) E + 3 = .494 E + 3 = 494

5) Therefore shift the addend right-
wards if needed and add the two numbers
— the mantissas— together.

6) Normalize the result if it is not
normal.

In binary floating-point the above addi-
tion of 456 4- 38 becomes:
456 is 137, 100,0,0,0

with a "true" form of 9, 228, 0, 0,
38 is 134,24,0,0,0
with a "true" form of 6, 152, 0, 0,
The augend is larger than the addend so
the numbers do not need to be switched
over, but there is a "difference" of +3, so
the addend has to be shifted three places
to the right to line it up with the augend.
Thus

456 stays as 9, 228, 0, 0,
whilst 38 becomes 9, 19, 0, 0,
The two mantissas can now be simply
added together to give the result
456 + 38 = 494 as 9, 247, 0, 0,
This result does not change with nor-
malization but with the exponent aug-
mented and the sign byte entered it
becomes finally:

494 is 137, 119,0,0,0
Note that, when an addition involves
negative numbers, the subroutine 2's
complements the negative mantissas, and
that, if the final result is to be negative, it
too will need to be complemented before
being placed on the "calculator stack."

multiplication

The subroutine for multiplication is
fairly straightforward. For two numbers
in floating-point form to be multiplied
together, the exponents are simply added,
and the bytes of the "true" mantissa are

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multiplied together bit-by-bit. The man-
tissas, being "fractional," when multiplied
together, decrease in absolute magnitude
and hence there is no danger of overflow.
However, the addition of the exponents
has to be checked for all the instances of
"underflow" — reaching zero — and true
numeric overflow.

The actual steps of the subroutine are
as follows:

1) Fetch the multiplier (the first number
of the multiplication) and return if it is
already 0; if it is not, form the "true"
mantissa.

2) Fetch the multiplicand (the second
number of the multiplication) and force
the result to be if it is already 0. If not,
again form a "true" mantissa.

3) Make available a set of registers to
hold the result of the multiplication and
set a counter to count the 32 times
required for the multiplication of a pair
of 32-bit mantissas.

4) Perform the 32 operations that pro-
duce the result.

5) Add the exponents, check for
"underflow" and "overflow," and finally
normalize the result.

As before, the algorithm will now be
illustrated with decimal numbers before a
binary example is given. Consider the
multiplication of 13 * 12 to give 156. When
converted to normalized E format, the
problem becomes
(.13 E+2) * (.12 E + 2) equals (.156 E + 3)

How is it done? Following step 3 above,
the result is set to be 0, and a counter set
for the number of digits in the mantissas—
in this case, 2. Then the following looping
is performed the specified number of
times.

The steps of the loop are:

1) Shift the multiplier rightwards and
note the carry.

2) Increase the result by the product of
the carry and the multiplicand.

3) Decrease the result by shifting it one
place to the right.

Now let us look at the example values:
1st loop

1) .13 becomes .01 with a carry of 3.

2) The result, presently 0.0, is increased
by 3 * .12 to become .36.

3) Decrease the result, by shifting right-
ward, to make .036.

2nd loop

1) .01 becomes .00 with a carry of 1.

2) The result, presently .036, is
increased by 1 * .12 to become .156.

3) Decrease the result, by shifting
rightwards, to make .0156.

This value of .0156 is the mantissa that
goes with the exponent obtained by
adding the "true" exponents, and the
result is presently 0.156 E + 4 which
upon normalization becomes .156 E + 3
which is the expected result.

In binary floating point 13 * 12
becomes

(132, 80, 0,0,0)* (132, 64, 0,0,0)
with the result 156 being 136, 28, 0, 0,

The "true" exponents of both 12 and
13 are 4, and the first nibbles (the first
four bits) of the "true" mantissas are
13: the bits 1101
12: the bits 1100
In this example for simplicity the multi-
plication will be made between two 4-bit
mantissas to produce an 8-bit result. The
full operation is 32 bits by 32 bits.

Now let us consider the loops.

1st loop

1) The multiplier, 1101, is shifted to the
right to give 01 10 and the carry equals 1.
1.

2) The result goes from 0000 to 1 100
and is itself shifted to give 0110.

3) The end multiplier bit was set, so the
present multiplicand was added to the
result before it was shifted.

2nd loop

1) The multiplier goes from 0110 to
0011.

2) There is no addition of the multipli-
cand, but the result is still shifted to give
00110.

3rd loop

1) The multiplier goes from 0011 to
0001.

2) The result is increased by adding the
multiplicand; 001 10 becomes 1 1 1 10.

3) This is shifted to become 01 1 1 10.
4th loop

1) The multiplier goes from 0001 to
0000.

2) The result goes from 011110 to
1.00111.

3) When shifted, it becomes 10011100
(8 bits given).

The exponents are now added and the
5-byte "true" number is formed as

8, 156,0,0,0
which, with the exponent augmented and
the sign bit reset, is

136, 28, 0, 0,
and that is the floating-point representa-
tion of 156.

Division

Of all the arithmetic subroutines, divi-
sion is the most complicated and the least
understood. It is particularly interesting

SYNC Magazine

to note that the Sinclair programmer
himself has made a mistake in his pro-
gramming (or has copied over someone
else's mistake!) for

PRINT PEEK 6332 ("unimproved"
ROM, 6351)
should give 218, not 225.

To divide one number into another in
floating-point form requires subtracting
the exponents and dividing the mantissas
bit-by-bit. Care must be taken to get the
correct exponent for the result because
there is a "borrow" to be taken into con-
sideration.

The actual steps of the subroutine are
as follows:

1) Fetch the divisor (the second number
of the division) and give REPORT-6 if it
is 0; otherwise, form the "true" floating-
point form.

2) Fetch the dividend (the first number
of the division) and form its "true"
floating-point form. A return is made if
the dividend is as there is no need to
divide into 0.

3) Set a counter to the number of bits
in the mantissas. In the actual 8K ROM
program the counter is used for 34 loops
as extra accuracy is sought — but then lost
because of the "programming error."

4) Perform the looping operation.

5) Subtract the exponents and adjust
for the "borrow" before, finally, normal-
izing the result as usual.

As before, the operation will be illu-
strated in decimal and binary arithmetic.
Consider the division of 486 by 3 to give
162 which, when converted to E format,
is (.4S6E + 3)/(.3E + l) = .162E + 3

So, the steps are:

First, set a counter to 3 as there are
three significant figures in the dividend.
Second, perform the following division
loop three times:

a) Subtract the divisor from the present
dividend. If it does "go," count the times
that it does and proceed. Else, restore the
dividend and proceed with the count at 0.

b) Rotate the "times count" leftwards
into the result, initially 0.

c) Shift the present dividend also left-
wards and note carefully whether or not
a carry is produced. If there is no carry,
go to 1 on the next loop; but, if there is
carry, then the divisor will definitely "go"
into the dividend, and this is done directly
before going to 2 for the next loop.

Now let us see the example values.
1st loop

1 ) .486 - .3 does go once, so make the
subtraction to give a new dividend of . 186
and a "times count" of 1.

2) Make the result 1.

3) Shift the dividend leftwards and note
that there is carry.

2nd loop

1) The divisor is now subtracted as
many times as it will go; i.e., 1.86 — .3
can be done 6 times and the dividend
becomes .06.

2) The "times count" of 6 is rotated
into the result which goes from 1 to 16.

3) The dividend is now shifted left-
wards, with .06 going to .6 with no carry.
3rd loop

1) The present dividend is divided by
the divisor, giving a "times count" of 2.

2) This "times count" is then rotated
into the result which thereby goes from
16 to 162. Strictly, this should now be
read as .162.

The exponents of +3 and +1 can now
be subtracted from each other to give
+2, the "borrow" taken into consideration
to make it +3, and the final result consid-
ered as .162 E + 3.

Certain of the above mechanisms are
difficult to explain in decimal arithmetic,
but, by repeating the operation in binary
floating-point arithmetic, I hope these
points will become clear.

In binary floating-point the operation
is 486 / 3 or

(137, 115, 0,0,0)/ (130, 64, 0,0,0)
with the result 162 being 136, 34, 0, 0, 0.
The "true" exponent for 486 is 9 and for 3
it is 2. In this case the division simplifies
to .11110011 /. 11000000
and there will be eight loops to consider.

1st loop

1) Trial subtract the divisor. It does go
once so the dividend becomes .0011
0011.

2) The "times count" goes into the
result to make it .0000 0001 and the
dividend is rotated to give .01 10 0110.

2nd loop

1 ) The subtraction does not go.

2) So the result becomes .0000 0010
and the dividend .1100 1100.

3rd loop

1) The subtraction goes, giving a divi-
dend of .0000 1 100.

2) The result becomes .0000 0101 and
the dividend is shifted to give .0001 1000.

4th-6th loops

1) On no loop does the subtraction

"go-"

2) Hence the result becomes .0010 1000
and the dividend is . 1 100 0000.

7th loop

1) The subtraction goes, leaving a
dividend of 0.

2) The result becomes .0101 0001.
8th loop

1) The result still has to be shifted,
although the dividend has been
exhausted.

2) It becomes finally .1010 0010.

The exponents are now subtracted: 9 -
2 — 7. The 'borrow" is considered to give
a final exponent of 8 and this makes the
result:

"true": 8, 162, 0, 0,
in Sinclair form: 136, 34, 0, 0,
which is decimal 162.

The reader is encouraged to try the
operations for any other values. Further
details of the arithmetic routines can be
found in Sinclair ZX81 ROM Dis-
assembly, Part B by Dr. Ian Logan and
Dr. Frank O'Hara. {Ed. — This work is
available from several sources. See the
ads in this issue. ) 5i

CHIRPER module for your ZX81

The CHIRPER module lets you enter keyboard
data fast and accurately. A sound can be heard
when a key has been entered enabling you to
spot a double entry or missed entry without
looking up at the screen.

The CHIRPER module lets you hear sound
patterns of a program running. Sound effects
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The CHIRPER module installs easily mside the
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ZX Destroyer

Raymond Fowkes

ZX Destroyer is a fast moving action
game which is written in a hybrid Basic
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the initial set-up and ending.

4K ROM Version

Loading the Machine Code

The machine code routine is placed in
a REMark statement at the beginning of
the program. Remember, whenever you
are working with machine code, save
frequently. It is hard to save too often!

1 ) Type in the lines in Figure 1 very
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another. Do not enter the spaces; these
are included only for your convenience.
Note also that the O's in lines 1 and 2 are
not zeros. It is suggested that you SAVE
after entering each REM line.

2) Type in the checker routine in Figure
2.

3) Press RUN and NEWLINE and wait
for the results.

4) Unless you are one of the lucky few,
the computer will indicate a mistake in
one of the four REM lines. If so, go back
and recheck your entry. Correct the
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the result is "PROGRAM OK," SAVE
the corrected version. You are now about
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will run correctly.

Raymond Fowkes, PO Box 336. Coalifiga < \
93210.

5) Enter the lines in Figure 3 over the
existing ones and RUN. The machine
code program has now been processed
and stored in line 1. Do not LIST line I or
press HOME! Doing so couid crash the
program and ruin all the work you have
just done. SAVE.

Entering the Basic Program

1 ) Erase lines 2-120 by entering the line
number and hitting NEWLINE.

2) Enter the program in Figure 4 exactly
as printed. This provides the set-up for
the game. SAVE again.

3) Press RUN and NEWLINE.

4) In the center of your display you
should see the alien space ship with the
alien in the middle of his control dome.
Two powerful rotating screens protect
the bottom of the ship. You will also see
the invader's laser moving back and forth
underneath the ship. It will fire when your
laser base comes into range.

5) In the lower left corner of the display
you will see a "$" which represents one of
your laser bases. In the upper left corner
the display will tell you how many func-
tioning lasers you have.

6) If the screen display does not match
the description in 4) and 3) above, go
back and check your Basic program or
reenter your machine code routine. If
neither of these works, wait for the next
Glitchoidz report!

8K ROM Version

The 8K ROM version is very similar to
the 4K ROM version and gives flicker
free action in the FAST mode.

Loading the Machine Code

1 ) Load the the machine code in Figure
6 as in step 1 in "Loading the Machine

Code" above. This code is a modification
of the 4K ROM version. Unlike the 4K
machine the 8K machine allows you to
LIST the REM lines without crashing the
system.

2) Enter the checker program in Figure
7. RUN the program in FAST mode.

3) After several seconds of processing,
the computer will indicate a "PROGRAM
OK" or a mistake in one of the first four
lines. If you have 2K RAM. editing
requires a special process. First. LIST the
line with the mistake. Then execute a
CLEAR command and EDIT when the
screen is cleared. You can then make the
correction and return the line to the
program by pressing NEWLINE. RUN
again and make any further corrections
needed until the result is "PROGRAM
OK."

4) Enter the lines in Figure 8 over the
existing lines. SAVE.

5) RUN the program. When it is fin-
ished, the machine code routine will be
processed and stored in line 1.

6) Delete lines 20-90 by entering the
line numbers and NEWLINE. Then enter
the lines in Figure 9. Line 10 causes CLS
to fill the screen wjth spaces. If you have
16K RAM, this is automatic, and you can
use this line as a place for the program
name. Lines 100-170 set up the display.
Lines 180-200 reset the laser indicators
and start the laser base at the lower left
corner of the display. Lines 210 and 240
should be entered only if your computer
can run in the SLOW mode.

7) Again SAVE. Then RUN. You
should see the same screen display as
above in the 4K version.

SYNC Magazine

Figure 1: 4K ROM Machine Code.

1 HEM 2^1 923 111 117 CY9 I ? A >7 «8D UT8 FXV
?2S N59 FrfV 22S NAA W^d MAA 9 CK 33X P7l *"TC JlX
UCn ?,C PIC 9^C F5? 28D UAK 1 T9 ETK QHH CFU K3Q
TIT 1Q5 UQG ?5a BCK 5SY CF5 729 A9C VA? -S <3 CDT
CXj 5DC *CG 6XT CK3 2k2 C6^ IY1 Q36 DUA ZFU K3?
Ui-V IY1 3FU QCI 3CT 3i v X XSE 7EG K3X S8C K63 Y8l
36D UAJ STG QY3 3AK 587 5HA 3PC G37 LXG CK3 C8

2 REM FUI CA, 7*K 1ZF UrI K13 271 CG3 XV7 1CK
31 H A1C G36 U8H UK1 IEB *53 7TG 67Z HUG IBS 97N
G6Z Kro H7L CG3 6lo £?K CG3 «NK 771 PHK \ZY. 3l±
973 VAK 1QH ?R9 T27 ZXQ CKB ^C6 643 IE3 Q3*

ZHU K77 P^H ACJ C7Q X2C KC7 3DU 101 Q/F 012 CIS

2JI XI Q MrU 9FO 5AJ 7BH ACr 6N3 8DU QK1 111 9?i'

X2S TiX 2KQ 187 K67 3D7 I VI KEH ACM 6RC r"6L ; U

3 HEM 211 ll6 111 ill 712 ?73 231 1~1 2^3 ll6
6l2 712 116 612 k?B 162 778 17^ 151 ^12 l 7 7 9 11
147*4- i?7 4i7 317 311 121 212 162 361 1^ 7^1 *11
6?6 212 ^?6 111 i?4 172 7^1 111 317 M6 311 616
311 716 576 115 7 9 1 121 7^1 111 173 1~1 122 ?U

OOO IT) 1 "7^

199 O 1 A

731 212 2l6 616 112 171 113 717 6ll 111 721 <*2

U REM 221 481 112 112 211 212 512 ?6l 171 1°

111 867 61? 322 2?1 178 1?1 116 7?\ ??.? 212 111

521 212 111 76l 212 111 76l 222 111 122 17° 111

213 182 111 S6l 631 HI 721 174 121 178 173 1 9 1

122 211 111 87? 113 127 211 n? 161 1>3 321 117

611 ill 43j 211 76i 111 873 111 9 1 9 1°1 1U 1 A 3

111 631 111 661 m 731 111 '11 874 1 ;47 ^1 A ?2

Figure 2: 4K ROM Checker Program

10 LET B=0

20 FOR A« 16426 TO 17419

30 LET B=B+PEEK (A) -PEEK iA+1 )

40 IF A« 16672 THEN IF NOT B«36
5 THEN GOTO 120

50 IF A-16920 THEN IF NOT B=65
THEN GOTO 120

60 IF A- 1/170 THEN IF NOT B»35
9 THEN GOTO 120

70 LET A=A + 1

80 NEXT A

90 IF NOT B=22 THEN GOTO 120
100 PRINT "PROGRAM OK"
110 STOP

120 PRINT "MISTAKE IN LINE*"; A/
249-65

Figure 3.

55 l<

\ 00

1 LO

1 20

LET B--= 16427
FOR A-16427 TO 16916
POT F_ A, PEEK (&) +PEEK (B+498) *
)44

LET B-B+l

IF B=166/2 THEN LET B=B + 4
NEXT A

POKE A+3,254
POKE h»^2,2
POKE A+l ,
POKE A, 1 18
POKE 16403,2
LIST 2

Figure 4: 4K ROM Basic ProRram

100 POKE 16421,24

110 PRINT "LASER#5##*####*WW"

120 LET BS»CHR*<131)

130 PRINT
*;B*| "W"

140 PRINT
D"
150 PRINT
16U PRINT

•#**t**w";B*;B*: "##";B

'##F";B$, "####" ;B*;

jCHR* (134

;CHR*< 134) ;

■*FE" , " "###tt»RD"
"#£#####" ;CHR*< 128) ;

"0##### M ; c;hr* < 136)

170 LET B*=CHR*(130)

180 PRINT ,&*;"######"
> ; "E#tttttt#*NJ"

190 PRINT , "0#####F"
CHR« ( 1 36 ) ; "' ###### M ; B*

200 PRINT , M u#*####SP#+**t##tt M ;B*
, "#### AAAAAAAAAAAAAAAAAAAAAAAA ",
"#ttti# AAAAAAAAAAAAAAAAAAAAAAAA " ,
FOR A-l TO 14

220 PRINT ,,, ,

230 NEXT A

240 PRINT

250 POKE 16429,0

260 POKE 16432, 177

270 POKE 16437,0

280 RANDOMISE USR ( 16439)

300 INPUT A %

310 CLS

33o RUN

_ Figure 5: Sample Opening and Ending. .

CLS
20 PR J NT , M ZX"

PRINT
40 PRINT

50 PRINT "SKILL: ##30»BEG INNER*
TO INEXPERT"
60 INPUT A

70 IF l:A OR A , 30 THEN GOTO 60
80 POKE 16428,^
90 CLS
3 1 F P P E K 1 1 6 4 3 7 ) ■ = 1 6 I HE N G I
540
310 CLS

■ PRINT "YOU WERE DESTROYED"
330 GOTO 4
340 INPUT B%

350 CLS

360 PRINT

*"
370 PRINT
380 PRINT
390 PRINT

400 PRINT
410 PRINT
PRINT

'*# INVADER DESTROYED**

'CRASH CURSOR"

'WOULD BE PROUD OF" YO

"N/L TO PLAY AGAIN"

July/August 1982

430 INPUT B*
440 IF &*="" THEN RUN
(or THEN RUN 90;

Note: To make winning more difficult,
add this and delete line 70 (to prevent
memory overflow):

210 FOR A«l TO 52

PRINT " + + + + 4+ + -*";
235 PRINT

Fi«ure 7: 8K ROM Checker Program.

Figure 6: 8K ROM Machine Code.

i REM G4.1R2E11I117CYQU2BSDUTS
aU2S7U7392305HU7392U2SMU73SNflRUV
SHRfi9CM33XF71PTCJlX4CM20CFlC94CF
5728DUflKlT9ETK0HRCF4K60TlT10SD0G
75XBCM55YCF5729R9CM4T5X30DTCX35D
09CG6XTCK3242C6dIY10S6DUMUUK67l, i
PPIY18UUOCI3CT3MXRSE7E6K6XMKCK6E
YS 1S6DURJSTGG074HRSFCG37LXGCK30

2 REM 8UUICRQ7UK1ZUUPIK1S271C
G3XU71CK31HR1CGB643YUK1IEBOS67TG
67ZYUCIBS77NG62MPSH7LCGB6ISE7KCG
BMNK27IPHK1CKB1P97RU9K1QH7R9T27I
XQCKB2C664BIEBOS6HURZYUK27P9HRCJ
C70X2CKC78DUIE20HF02201S2JIX10HF
09F0SRJ7BHRCP6NB8HU0K1I119TYX2ST
IX2K0187K67SD7IU1KEHRCM6RCF6L7U

2© REM 2X1317111113.7142782126©
11 12866 1211 12766 1211 1276612478 ie
2778174.1514.12127211474-1274-173173
11121212162361144741211626212426
11117417274111131741631161631171
65761157211217411111731211422111
13111242172176141221116211177217
1117312122167611182176111117214

30 REM 24214811121142112125127
61171272111867612324221178121116
22142721211162121211176121211176
12221111221721112131821118616311
11721174128178173121142211111872
11312721121211114332111761111143
32 11761 11 1873118212121 11116311 15
3111166112173111121187414741652

50 LET B=0

60 FOR fi=16509 TO 17516 STEP 2

70 LET B=B+PEEK R#(PEEK CR+i)-
1)

80 LET C= (fi-16507) /126

90 IF C=2 RND B0 243529 OR C=4

RND BO488Q40 OR C=6 AND B<>61£
608 THEN GOTO 140

100 NEXT R

110 IF B0 733561 THEN GOTO 140

120 PRINT "PROGRAM OK"

130 STOP

140 PRINT "MISTAKE IN LINE ";"1
2 2030" (C-l TO C)

Figure 8.

10 REM

20 REM

30 REM

35 REM

4© POKE 165 21,244-

5© POKE 16512 . 1

60 LET B=165I4

70 FOR R=B TO 17005

80 IF 8=16760 THEN LET 8=8+6

9® POKE A, PEEK B + PEEr: VB + S04.* tf
35-1044

100 LET B=B+1

110 NEXT R

120 POKE 16511,233

130 POKE A+5,234

14© POKE ft +4 ^

150 POKE ft+3.2

160 POKE A+2.10

17© POKE A+l,e

180 POKE ft . IIS

EVEN IF YOUR LIGHTS GO OUT
YOUR COMPUTER WON"

Introducing

NiCd Battery Back-Up Units from Syncwware

PRICES:

Baby BBU — 39.50
BBU-1 — 54.50
BBU-2- 84.50

• Make your ZX Portable
BBU-2 runs over 2 hr.
BBU-1 runs 1 hr.
Baby BBU runs V4 hr.

• Make your ZX immune
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• Protection against
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fuses, etc.

TIRED OF LINE GLITCHES

GIVING YOUR COMPUTER AMNESIA?

Let Syncware take the annoyance out of computing. Baby BBU and BBU-1 use ex-
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BBU-2 contains built-in heavy duty power supply,
eliminating need for original supply. In addition,
BBU-2's output is pre-regulated at 8 volts for addi-
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Prices are postpaid in continental
U. S. Foreign orders — add $5. 00.
Payment must be in U. S. cur-
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international M. O. only.

SINCLAIR/TIMEX USERS

NOW SYNERGISTIC OFFERS YOU THE SMART™' CHOICE
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THE SYSTEM LOGIC KBD-I

SMART™' KEYBOARD

ENHANCEMENT FOR

SINCLAIR/TIMEX

COMPUTERS

* •% 4. 4m m» dh +'+ mm mm ■
m% mh Jm A mm mm —

SYSTEM LOGIC — KBD-1

The System Logic KBD-I Keyboard en-
hancement offers Sinclair ZX-80, ZX81
and Timex TS-100 users an intelligent
keyboard peripheral.

A KBD-I allows an increase in user
throughput by as much as 70% while re-
ducing fatigue factor errors.

Now enter data and programs quickly
without having to 'hunt' for key contacts.
Each key produces 'tactile' feedback in
addition to employing right-and left-hand
'smart' shift keys. The KBD-I remains in
the shifted mode with a single keystroke,
while exiting from the shifted mode with a
second (left or right!) keystroke entry.

The KBD-I simplifies integrating your
computer system into a professional or
business application. The compact size
of the KBD-I permits easy portability, its
brushed aluminum black anodized cabi-
net is a cautious blend of attractive
design and the highest quality engineer-
ing and manufacturing techniques.

SMART ™ features
Patent Pending

FEATURES

• SMART™' shift function

• Tactile feedback

• 59 keys (with left and right shifts)

• Standard (QWERTY) typewriter format

• Silk screen labels compatible with
Sinclair/Timex keyboard

• Compact design

• Rugged yet attractive black anodized
aluminum cabinet

• Simple installation

• Custom engineered for Sinclair/Timex
computers

SPECIFICATIONS

Contact resistance: 20Q @ 1 mA
Contact rating: 1.0V/ A
Contact bounce: ^S.OmSec.
Switch life: 5.0x1 6 operations

typical
Switch force: < 9.0 oz.
Switch travel: .01 5 in.

MAIL ORDER TO:

SYNERGISTIC DESIGN

P.O. BOX 41 1023
CHICAGO, ILLINOIS 60641

•Illinois residents include
6% sales tax.

SYSTEM LOGIC KBD-I KEYBOARD

PRICE

$89.95*

QTY.

AMT.

Shipping and handling (per unit)

$ 4.95

Money order or check TOTAL

NAME

ADDRESS_
CITY

.STATE.

_2IP_

.Figure 9: 8K ROM Basic Pro R ram.

10 POKE 16389,128

90 CL.S

100 PRINT "LASER 5";TQB 15; "^

110 PRINT TAB 12; *W~ ^^■"

120 PRINT TRB 10; ■•^■» ; TRB 20;"

130 PRINT TRB 9;

14.0 PRINT TRB 9;

150 PRINT TRB 8;
I
160 PRINT TRB 8;

170 PRINT TRJ^B
t;;TRB 4-; " r "~
Tl;TflB 4.;

• * ";TRB 21;

V ■

180 POKE 16516,0

190 POKE 18519,223

S00 POKE 16524- ,0

210 FRST

220 RRND USR 16526

230 PRU3E 99

24.0 SL.QU

250 RUN

The number or letter indicates the key
on which the graphic is found and the
number in () gives the number of times to
press the key.

1 00 < 2 ) 6

110

(2) 1\ (2) 7;

1 20

7; 7; 4

1 30

1; 2; 4

140

space; 5; Y

1 ^j'O

1 60

3; R; Y; 8

1 70

T; 4; 8; (24)

(24) A

To changei

4K ROM

8K ROM

Number o-f 1

aser basest

Change the number in 1 ine

110

100

Speed o-f al

ien's laser:

POKE a number -from 1-30 into

16428

16515

Speed of al

ien's screens;

POKE another number into

16830

16919

(It is 6

now; try 1 or 2)

Laser base

graphic!

POKE new c

haracter code into

16621

16716

and into

16904

16993

Alien's laser graphics

POKE new character code into

16527

16622

Fiiiurell: Variables.

Decimal

Initial

Address

d:(lX + di Setting

Function

16^27

o 50

skill variable

l64?8

1 3

skill set

laser Indicator

16430

3 8

trun t;ositl

^ 1

gun direction (1,-1)

16UJ5

5 177

base cosltton

lqser position

l6bjk

laser cosltl^n

1**35

"shell" po

si tion

l6fc>6

"shell" position

"shell" indicator

It 6

rotate counter

NOW AVAILABLE

Keyboards

Standard Computer Keyboard Designed
for ZX81 , ZX80, & Micro Ace

• Same switches used on Apple Computers
• Two shift keys • 6-inch space bar

Plans for keyboard conversion with reverse video —

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Keyboard with complete parts and plans - $55.00

Wired keyboard, complete with plans — $75.00

Shipping Charge (by UPS) - $5.00

SEND CHECK OR MONEY ORDER TO
SEND SASE FOR INFO

Prices Subject To Change

LJ.H. Enterprises

PO Box 6305 Orange CA 92667
(714) 780-U22 Visa& M C Accepted

THE EXPLORERS

GUIDE TO THE

ZX81

If you have ZX81 then you need this
book (120 Pages).

1 K and 1 6K Programs.
Games and Application.
RAM and I/O Circuits.
Programming Hints
ROM Routines.

$11 from:

TIME DATA
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Califon, N.J. 07830

Enclosed

Name

Address

City

Check/M.O.

State

Zip

SYNC Magazine

FULLER FD SYSTEM $79.95

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INSTALLATION

Simply unscrew the ZX printed circuit board from
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MOTHERBOARD:

We also manufacture a mother board which allows
expansion to the ZX memory and I/O facilities
WITHIN the case, as well as our power supply unit
and reset switch.

AD Code

Price t

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Fuller FD System 42 Keyboard & case

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29.95

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49.95

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14.95

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Name

Address

t US Dollars City/State/Zip

K AVAILABLE NOW S

HINTS a TIPS for the ZX81

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*80 pages explaining clearly how to squeeze a computing quart out of a
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"Understanding the Display File - using the display file as memory clearing a
part of the display, using tokens in PRINT statements

"Converting ZX80 programs-explaining simply but comprehensively how to
convert the hundreds of published ZX80 programs

"Chaining Programs- revealing techniques for passing data between programs
calling subroutines from cassette and establishing data files
* Machine Code Programs— all you want to know about Z80 machine language
Explaining how to write load edit and save machine code and how to debug
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Routines and programs are scattered liberally throughout the text and the
final chapter consists of twelve useful, interesting and entertaining programs
such as LINE RENUMBER, BOUNCER, SHOOT STATISTICS etc
Cassettes for 16K ZX81

SPACE INTRUDERS-fight the marauding alien as you battle to save the
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Cassettes for 1K ZX81

"MINI SPACE INTRUDER'-now available for IK machine $11 95

STATISTICS - Mean standard deviation regression, trend analysis, chi squared
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Z80 Op Codes -this handy ready reckoner lists all 600 plus Z80 machine
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mm& H, & Ds M m K th i 5 ta PM d

FR = 3 292 E 05 6E = 1 297 E 03

TX= 8 275 E 05 X= 5 222 E 05
TY= 1 182 E 07 Y = -2 574 E 05
TZ = 4 780 E 06 Z = 5 692 E 06

16K
RAM

The Federation has
declared a state of allout war.
leaving you in charge of the
Starship Defiant: newest and
most advanced spacecraft
known to man

Soon, your experienced
guidance will bring you within
range of the Klingon convoy
Hundreds of stars flash by as
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Phasors, Shields, Masking,
Navigation, Scanning, and
Computation Equipment. Tne
energy drain is tremendous, as
the target distance indicator
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As you come into range
you set your cross-hairs on the
nearest ship. Fire Phasors' ! '
Switch to Aft view' ! ' Evasive
Maneuvers' ' ' Space explodes
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the remainder lock onto your
position..

High speed graphics and
custom ML math package
provide the real time, accurate
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You've never seen this kind of
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residents add $ 95 tax)

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ELECTRONICS

959 East 460 South
Provo, UT 84601

Label

JTART

Variations

Variations can be made in both ver-
sions. Figure 10 summarizes some of the
main possibilities. If you have extra RAM,
you can add your own openings and
endings such as suggested in Figure 5.
Note that PEEK 16524=16 can indicate
to a program that the invader was
destroyed.

British TV Differences

Since the speed of British television
receivers is different from that of U.S.
receivers, some adjustment may be
needed. If this adjustment cannot be
made with the vertical hold, then some
changes in the program need to be made
to slow down. For the 8K ROM try POKE
16538,79, and POKE 16556,79; for the 4K
ROM, POKE 16455,80, and POKE
16464,79. These will slow it down quite a
bit, but other values may work better.
{Ed. — SYNC would be interested in
hearing from British readers concerning
their experience with this problem. )

Playing the Game

The goal of the game is to blast through
the bottom protective screens of the alien
ship with your lasers and hit the alien (the
left foot). This will destroy the alien and
his ship. The game begins when you
launch your attack on the alien ship from
your laser base. Since both your laser and
the alien's laser fire only on the perpen-
dicular, you must get your base in position
to hit the ship. To move your base, press
the arrow keys: 5 for left, and 8 for right.
To fire press or 1. Your laser has an
unlimited number of shots. The alien's
laser has computer controlled accuracy
and will destroy all five of your laser
bases if you are not careful. So watch
out!

The game is over when you have
destroyed the alien or when you have lost
all your laser bases. When the game is
over, you can play again by pressing
NEWLINE. If not, press NEWLINE and
BREAK and you will return to Basic.
You can also BREAK at any time during
the game, •%

Flsure 12: Z80 Instructions (4K ROM)

Instruction

LD IX, 16^+27

0U? (25*0. A
LD A, 73
LD B t ?5
LD HL, (16396)
3ST ?,H
LD C,3°
CALL <±32
LD A, ■>)?

DSC AL

LD C,3l
CALL 432
LD A, 127
IN A, (25M
BRA

Comment

Index register points to variables
display one fraTe

set Tusk for 3RrJU\. key

re«*d ke.v board

push break bit Into c-rrv

SYNC Magazine

Label

Instruction

Comment

returi

ree, I

S«J

-. . 1 ■

-.35

■

ttecr<

TOV(

. - : )

• A

. .

E r

*,1

. .

- i

HL ) ,

e~as<

push off Mt

Lb A.C

put old Bointsr into A

upda *

• '),A

» :e pointer

ve. pointer 5 spaces

3LA £

dL , Jc

LJ A,

load A with "nev.'llne"

COTIpft •

sync

. .

reverse direction If necessary

zet • ion

NcJ

fce It

• 1 . a

reels

svnc

:,A

:.ut into C

...Ar '

save It

L3 fc,(IA+3)

set ?un position

P *.c

• "left" kev

add ■

•ri^htr key

sub'

1a + 5)

co~ ; tion

bescln laser If aun In ro-ntlon

■ 1,1

set

LO L, (IXO)

■

Inta to Usolay

LD (!6Ujj),HL

fill

[ ,(16*33)

tret • J nn

lr.c-ement lndi

erase lo--

chec-

sync

Ci (HL)

LD (HL),?

fill -

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A PORTABLE COMPUTER SYSTEM

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And The TV Adapter.

$149.95 Includes Shipping & Handling.

Kansas Residents add 3% Sales Tax.

TO ORDER

SEND CHECK OR MONEY ORDER

MOHR & ASSOCIATES CORP.

645 N. Baltimore

Derby, KS 67037

(316)788-1526/788-3165

MC/VISA ACCEPTED

Bridge SoPtware
Qua 1 i xy SoPtwar e

r • ■ tic

12Z2J1 Xj

.0668-

"bom;

thtJa I* n °66M Hill

Some UK customer reepons*

"I have oought numerous other items of software Yours ere

euceeeni Thev LOAD wee*, have perfect >nstruct/ons

the most user-fnendty / have ever met (P R Notts}

very pleased to fmd the program toed first time end olav §
creditable version of invaders Please supply MVL TlGRAPHlCS '

(M Z Cumbna)

Enfoymg GAMES' very much - Letter Square' >s quite
addictive "if W Manchester)

Many thanks for the Stahshcs programme. I am wee" pleased
wtth it "(AM Herts)

IK GRAPHICS (Keleidoscope. Large Print. Medium Print, Drew i

Picture). Manual nnfy (contains accurate Ratings, notes,

information and ideas!... C4.50/$9

Package of cassette end manual t&00/$12

IK GAMES (Duck Shoot, Moonlander, Hangmen. Crossword.

Letter Square). Cassette end instructions C4.SO/S9

16K GALAXY INVADERS «\ machine code. Cassette an6

instructione ( 16K RAM pack needed) £4. 50/$9

1WC MULTIGRAPHICS - crests drawings, advertising display*.
etc. on screen. Displays can be saved on tape, printed on your ZX
printer. Cassette end instructions f'oVC RAM pack needed/,. .Cfi.00/$12
IK STATISTICS - cassette end instructions £4.50/99

Prices include Air Mall Send £ or. $ check.

BRIDGE SOFTWARE (S)

36 FERNWOOD. MARPLE BRIDGE
STOCKPORT, CHESHIRE SK6 5BE ,U.K.

July/August 1982

SOFTWARE

and

ZX81 SUPPLIES

TIM EX 1000

GAMES, EDUCATION, HOME OR BUSINESS APPLICATIONS

Choose from our Extensive collection of over 100 programs,
far too many to list here so if you don't see something you
like, send for our catalogue, $2.25 handling and --credit on
GAMES y° ur f' rst purchase.

mazogs HOME-SAVINGS

A large complex maze which contains a glittering and fabulous
treasure, you not only have to find the treasure and bring it out of
the maze, but face the guardians of the maze in the form of fear-
ful MAZOGS. Even if you survive you could starve to death if you
get lost. 3 levels of difficulty, only $29.95 16K

GALAXIONS

Features of an arcade game. Attacks-Defends and keeps per-
sonal scores, only $14 95 16K

BATTLE SHIP

Play against the computer to destroy its battle ships, cruisers,
destroyers, etc. only 10 95 16K

VOLCANIC DUNGEON/HANGMAN

1. Attempt to rescue the elfin princess: mystical monsters, pits,
fireyheavens. Reducing strength and water make the quest
anything but easy

2. Deluxe version of the classic game, play against second per-
son or computer with 400 word vocabulary, only $10 25 16K

ALIEN INTRUDER/HIEROGLYPHICS

1. You find you are the only survivor on the Explorer Class III
star ship. Try and escape before you fall victim to the alien mon-
strosity that destroyed the crew.

2. Decode the ancient 39 symbol alphabet in time to save a
famous explorer, only $10 25 16K

WUMPUS ADVENTURE/MOVIE MOGUL

1. 1-4 players seek the famous creature in the most famous and
dangerous Wumpus hunt ever.
Features: Super Bats. Pits, Tremors. Swamps, Magic Arrows.

Giant Sea Serpents. Wumpus Muk and Magic Springs.

2. Guide making you through the often hilarious traumas of

production. Use your budget wisely to make a fortune, only
$10 25 16K

GREAT UNCLE ARBUTHNOTS INHERITANCE

You are left $100,000 but first must turn $100,000 of it into a fur-
ther $100,000 by investing in the British Stock Market and Metal
Exchange in 26 weeks. You then have a further 26 weeks to
make $100,000 running a soft drink factory, only $70.25 16K

GREAT BRITAIN LTD.

You are the Prime Minister and Chancellor of the Exchequer of
Great Britian. Your aim is to stay in office as long as possible.

$10 25 16K

AROUND EUROPE IN 80 HOURS

You have a bet of $20,000 to visit 12 capital cities in Europe in
two and a half days, travel agents permitting, only $10 25 16K

FINANCE I

Balance and maintain checkbook. No overdrawn or returned
checks, only $9 95 16K

HOME PLAN I

Keep your diary in order, only $8 50 16K

DATES

Keep track of your food and freezer needs, only $9.95 16K

APPLICATION PROGRAMS

TOOL KIT

Provides many special features (line number, search and
replace, free space, etc.) plus special graphics mode and tape
routine, only $10.25 16K

GRAPHICS TOOL KIT

22 exciting Machine Code routines that give you control over
your screen as never before, only $1025 16K

MICRO-MUSIC

Convert your keyboard into an organ mantle, only $8.50 16K

EDUCATIONAL - Learn

CHESS I

Six levels and analysis options, only $72.95 1K

CHESS II

Seven levels and a recommended move option, only $24 95
16K

ZX-BUG

30 in 1 tool. Disassemble. Access all registers, search, modify
memory with cassette routines, only $74 95 16K

BUSINESS - Opportunity

ZX-99 TEXT

Fantastic word processor with output to your printer through our
ZX-99. $29 95 16K

BASIC BUSINESS I

Cash flow control and planning. $76 95 16K

Coming in the next issue:

HIGH RESOLUTION GRAPHICS BOARD AND COLOR
All for your ZX-81/Timex 1000
DEALERS WANTED/INQUIRIES WELCOME
data-assette". 56 South 3rd. st. Oxford, PA 19363
1-800-523-2909
1-215-932-3626

ZX81 or TIMEX 1000

data-assette

Your One Stop Shop
All Products Guaranteed

EVERYTHING YOU WILL NEED!! ADD ON TO YOUR ZX 81ATIMEX 1000!! ALL PRODUCTS 100% GUARANTEED !!
NOW GROW YOUR SYSTEM AS YOUR NEEDS CHANGE, AND WE WILL GIVE YOU PRODUCTS, SERVICE, SOFT-
WARE AND ADVICE. WE HAVE BEEN IN THE BUSINESS IN ENGLAND FOR OVER ONE YEAR AND OFFER THIS
EXPERIENCE TO ALL OUR CUSTOMERS.

New Low Prices

1st STEP - MEMORY - RAM

16K - 32K or 64K
$59.95 - $109.95 or $149.95

Each RAM extends the BASIC memory to provide the user space for
all applications.

2nd STEP - KEYBOARDS
FULL SIZE or MINI $75.00

3rd STEP - ZX-99

TAPE
CONTROL

Now add Real ■DATA-PROCESSING power to your ZX-81 with our
sophist. cated extension. Provides FULL SOFTWARE CONTROL of
four (4) tape decks and a PRINTER interface for any RS 232 Serial
Printer, giving full 132 ASC II characters of output. Plus!!!!!!

* * AUTOMATIC TAPE TO TAPE COPY

* * TAPE BLOCK SKIP. DIAGNOSTIC ASSISTANCE

INTRODUCTORY OFFER "$375.0CT

Special to New Owners, show us your invoice and order in 30 days
from the date. We will give you this FULL PACKAGE for the low
price of $300.00. 64K RAM + Keyboard + ZX99. Add it to your prin-
ter and for under $400.00 you have full MINI-CAPABILITIES.

Real Professional KEYBOARDS Computer Size and with special
features like!!!!Repeat Keys on the full size. Both units are easy to
install at home . Supplied with cables & instructions.

BLANK CASSETTES

C-5 $.69

C-10 $.74

C-12 $.77

C-15 $.79

C-20 $.84

C-25 $.89

* * DATA RETREIVAL WORD PROCESSING

* * RS 232 C Serial Printer Interface
EQUALS REAL MINICOMPUTER CAPABILITIES

data-assette

Charge to

| visa mastercard

■ account number

Please ruih me

Quantity Price Total

56 South 3rd Street |
Oxford. PA 19363 | ^ Blf * gg "

Signature

Telephone Orders
1-800-523-2909

In Pennsylvania
(215) 932-3626

I
I

| : .v.

| NAME

| ADDRESS .

I —

rzzi

SHIPPING

TOTAL

Send me details.

Software
Supplies
User Clubs
J Local Dealers
New Products
Hi-Resolution or Color Boards

plus Shipping

SYC-1

STOCK MARKET

PRICE

ANALYSIS

HELP! for the
Small Investor

Now SINCLAIR 2X-8 1 { 1 6K) owners can do what the professional market traders
do — use a computer to predtct price direction Th»s program tracks up to six stocks,
averages, or commodities, and produces graphs and uses technical indicators to
help you make trades

Technical analysis is based on two ideas first, that the market, like the rest of
human behavior, repeats itself, and second, that there are professionals and in
siders who know what the market is going to do before everyone else does, and who
place trades in a way that is hardly noticeable TECHNICAL ANALYSIS attempts to
read the pnce action and volume figures to determine whether predicate patterns
are developing, and what the professionals are doing

Professional traders have been using computers to make this kind of analysis for
years, because the manipulation of the data is very complicated and time-
consuming With this program, you let the computer do the work, and its signals
become a powerful investment tool

The program makes GRAPHS of the daily pnces. of two moving averages, and of
a volume indicator A booklet that comes with the program helps you learn what to
look for

The program does an ANALYSIS to signal trend-formation and turnarounds It
gives a score for each indicator, and a total score, to help you see whether there is
confirmation among the signals

USE THIS TO TRADE STOCKS. OPTIONS. AND THE NEW STOCK INDEX
FUTURES!'

This gives POWER TO THE SMALL INVESTOR!

For program tape and booklet send $30 00 to

NOOTER STOCK PROGRAM
320 East 25th Street
New York. N.Y. 10010

(N.Y. residents, add $2 48 sales tax.)

ZX80/ZX81 Keyboard

Full size 40 key keyboard. All symbols marked in two
colours. Proper typewriter style keys. Old keyboard,
RAM pack and printer still work.

Kit £10.04
Built £21.65

In/Out Port

24 line— controlled in BASIC. Drive motors, printers
etc. Input or Output.

Kit £11.74
Built £13.87

Motherboard

Drives RAM pack, printer and two other boards.

Kit £14.09
Built £16.08

Cash with order please. Postage (surface mail) £2.00
per order,

Also many other boards and connectors. Please send
for free illustrated catalogue.

REDDITCH ELECTRONICS
21 Ferney Hill Avenue

Redditch, Worcs.
B97 4RU ENGLAND.

Figure 12: Z80 Instructions (continued)

Label

BITE
H&ScT

Instruction

JR NZ,*IS6ED

EXX

L~ (IX+5M77

LD HL.7

LD BC,(l^jl96)

ADD HL.BC

DEC (HL)

LD A,?8

Cr (HL)

RET 2

LD HL.689

ADD HL.BC

LD (HLM3

EXX

LD B,U

DJNZ -2

LD A,l»*

CP (IX+2)

LD 3,20

Jrt NZ, REPLACE

LD (IX+2), 128

LH HL,(l6U33)

LD DE.-396

ADD HL.DE

LD B,3l

LD ( HL ) ,

LD (l6433).HL

JR SH

LD (HL),0

LD A,(1*U)

LD 3,35

CP (IX+2)

JR N2, REPLACE

LD B,35

LD (IX+2),0

DJNZ -2
X0R A
CP (IX+10)
JR Z.READ

LD HL, (16U35)
LD ( HL ) ,
LD DE.-33
ADD HL.DE
LD A, 2
LD 3,26
CP {HL)
JR Z,hi.SET
LD (l6<+35),HL
INC (IX+10)
LD A, 8
LD 3,22
Cj- (HL)
JR Z.
JR C.3ITE
LD A, 16
LD 3,20
CP (IX+10)
JR Z, RESET
LD A, 13
LD B.19
CP (IX+10)
J.i C, ROTATE
LD (HL),6
LD B,l?

TAFc
^u (HD,0
LD (IX+10J.0

TAIa

LD B.80
LD E.-2
LD (HL),0

Comment

s-*ve the resclste-s
replace laser Vise st le't

HL oolnts to (D-PILE)+?
one les lase- base
check for "zero"

return to BASIC if Te'-o

point to bottom left of screen

fill with bqse character

restore registers

sync

tl-slng loop

check for laser at bottom

sync

Indicate laser ending
get old Iqser poin'e**
tiove up 13 lines

sync

erase top of *l«ser bea"i"

update pointer

continue erasing laser
check for laser fully erased
sync

tlmlna loop
zero A

conpare shell Indicator

HL holds shell oir.'e-
e^a^e shell
nove u~ ore line

check for l^se*- hi" ahell
sync

update p^lnte 1 -
increTient counter
check for shell hit slier
sync

if shell hit alien
if shell hit sMr
check for shell at %
svnc

don't show shell if i hel-
(so shell isr't car^l^d awav

by rotation st hottOT of shir)

fill new shell locstl~n

take chunk out of shi-
re set indicator

loop 80 tl-rres

DE=-2

erase a character

SYNC Magazine

Label

Instruction

Comment

ADD HL.DE

move left 2 spaces

DJN2 AGAIN

do qgaln for exploding effect

return to BASIC

HEAD

EX AF.Ar'

get keyboard re^rUmr

0,A

test •fir©"

LD B,3<+

sync

JR NZ.SAVE

LD (IX+10J.1

set shell Indicator

LD L.UX + 5)

HL hol^s relative base position

LD H,?

Lj D3,->3

-nove up one line

ADD HL.DE

>C, (16396)

BC points I : 'He

IL,BC

adjust HL

LD (l64j)5),HL

update pointer

LD (HL),6

fill with shell character

-.2^

sync

oA/E

EX Ar.A.-' 1

replace keyboard reading

ag ta te

DJN2 -2

syncronlzatlon loop

DiC (IX+11)

decrement rotate counter

.95

sync

JR KZ, SLIDE

LD (IX+11), 6

restore rotate counter

LD -iL, (16396)

point to display file

LD DE.198

AJU HL.DE

HL points to t-'P left of 1

of ship

. ( HL )

first character

LD D.H

INC rX

HL=DE+1

LD BC.23

shift 23 spaces

LD (D*),A

replace fl**st chR^acte^ *i rlahl

iove to bottom riaht

EL . DE

LD A, (HL)

save last character

LD E..L

j£=HL

DSC HL

: ', ■' J

shift ? 3 spaces

LDDH

>E) t A

tee last cha "act-

sync

DJNZ -2

LD S.(XX+5)

LD HL,( 16396)

timing loop

ADD HL, L£

HL holds base

L ) ,

erase base

LD Dc,0

zer

EX A

r ■ re* A ' nj

BIT U.A

tes*-

DEC

dIT ',A
J.1 NZ.LEFT

test "rl*ht" key

INC DE

DE=0 or l If "right" pressed

LcrT

4DD HL.DE

move right or left

XOR A

zero A

OR (HL)

test for space and reset ca'-rv

1,19

sync

sac

■nove back

1.17

sync

B.O

zero addend

MERGE

LD (HL), 13

replace laser base

DJNZ -2

tiniing loop

LD A,(Ia+5)

get old pointer

ADD A,E

update,

(IX+5).A

and replace

JP DISH

Jump back to beginning

July/August 1982

PREMIUM

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LENGTH 12PAK 24-PAK

C05 $ .69 $ .59

C-10 $ .79 $ .69

C-20 $ .99 $ .89

C-30 .$1.19 $1.09

C-60 $1.49 $1.39

C-90 $1.79 $1.69

* CASES $ .21 $ .20

'Cases recommended to protect sensitive cassettes.

UPS SHIPPING
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MICRO-80™|NC,

2665 Buzby Road

Oak Harbor, WA 98277

— Distributors Wanted—

' 3-Fnrt

l/D board

for Microace,

ZX-80,81

16KRAM

edge connector

Programmable 8255 P. I. A. can
be coniigured for direct I/O;
polling of peripheral devices,
vectored priority interrupts.

Use it with A/D converters,
serial I/O port chips, relays,
sensor inputs, clock chips, or a
security system.

Play chimes with different tunes
using your computer.

8080 M/L programs, TRS-80
M/L programs will work.

Literature available with
experiments, programs, and
information on how to use the
8255 P.I A

Basic 8255 board $50

add-ons extra

Professional Electronics

2X81 Software Plotter 1 — A sophisticated routine

that plots and graphs any function

(16K)S999(U.S)

Two Handed Euchre — Challenge the computer in this

entertaining and skillful game. (64K) $14.99 (U S )

J.C. Software

28 Shipley Rd

Weston, Ontario. Canada

M9R-3H8

EDUCATIONAL SOFTWARE (ZX 81 , 16K) on cas-
sette. MATHS for 14-17 year olds (3 full pro-
grams). MATHS and ENGLISH for 8-1 3 year olds:
4 cassettes, 6 programs per cassette, each with
jackpot game plus certificate. $9.50 per cassette
plus $4.00 total for mailing. ROSE CASSETTES,
148 Widney Lane, Solihull, West Midlands B91
3LH. England.

ZX-81/1K

LISTINGS OF 5 GAMES — $2.00

Z— GAMES

P.O. Box 367

Ringoes, N.J.

08551

RAM EXPANSION

ADD ON RAM FOR ZX80. 2K INCREMENTS I II
16K COMPLETE SCHEMATIC. PARTS LIST
SOURCES AND HOW-TO FOR $3 95 APPH
COST FOR 2K $20 FOR THE FIRST 2K Si 3 50
FOR EACH ADDITIONAL 2K NO ADDITIONAL
POWER SUPPLY NEEDED SEND S3 95 WITH
SASE TO

DENNIS WEBER B^
TROUTMAN N C 28ibb

4K ROM; IK RAM

Galaxy
Invaders

Phil Gervais

In Galaxy Invaders you are under
attack by a fleet of enemy spacecraft
which you must destroy before they
destroy you. This game uses the ZX8(Ts
IK RAM, graphics, and screen blackout
characteristics to produce an arcade type
game. The program (see Listing 1) is fairly
simple, but it employs techniques which
are used in the popular arcade games: 1)
insufficient information (you know they
are coming, but you do not know when);
2) the ability to play all day (if you are
good enough); and 3) a running point
total (for self-satisfaction).

A typical game goes like this: First, the
title block appears. You climb aboard
one of the three attack ships in your
squadron, prepare yourself for the worst,
hit NEWLINE, and blast off into space.
Suddenly, you see the enemy ships
approaching! You immediately hit your
firing button (NEWLINE) as quickly as
possible. The enemy craft disappear
quickly, but not before you hit one of
their small reconnaissance ships with a
deadly phaser. Your onboard computer
evaluates your shot. Each ship you hit is
worth either one or two points. Since
your objective is to destroy as many ships
as possible, a high point total is the
measure of a successful mission. Your
new point total is displayed along with
the number of ships you have hit. NEW-
LINE returns you to outer space for the
next round of the battle.

We must note some of the features of
the equipment that shape the battle strat-
egy. Both squadrons are equipped with
advanced radar firing which insures pin-
point accuracy. However, the enemy's
phasers are capable of jamming your
detection gear and vice versa. This insures
your accuracy and disrupts the enemy's
firing.

The scores in this game generally range
from 50 to 100. If you get over 150, you
rank among the best space pilots in the
galaxy. However, if you do not seem able
to win a battle, you will have to have your
engineers redesign the capability of your
attack ships by increasing the value of C
in lines 80-90 by 20 or more.

For those who have more than IK
RAM the step in Listing 2 gives a bonus
ship at 250 points.

May the luck of the galaxy warriors be
with you! 5

Phil M. Gervais, 714 5th Ave. South, Clinton, I A

52732.

Listing 1: Galaxy Invaders; 4K ROM, IK RAM.

RANDOMISE

CLS

LET P=0

LET Z=3

PRINT , "GALAXY INVADERS"

GO SUB 76

CLS

FOR 1=1 TO 20*RND<10O)

NEXT I

POKE 16414,0

POKE 16415,0

GO SUB 70

LET A=PEEK< 16414)

LET B=PEEK< 16415)

LET C=256*B+A-4

CLS

IF C<8 THEN GO TO 62

IF C<9 THEN GO TO 94

IF C<13 THEN GO TO 97

PRINT "YOU WERE HIT BY PHAS

ER"

LET 1=1-1

IF NOT Z=l THEN PRINT Z;"#S

U T PC

l CT(TT"

IF Z=l THEN PRINT 2; "#5HIP#

LEFT'

IF NOT Z=0 THEN GO TO 101

PRINT "POINTS ACCUMULATED: #

„. p

PRINT "START OVER IN NEW GA

i_!-i A i :

INPUT W*

IF CODE (W*) =62 THEN RUN

CLS

STOP

PRINT "DESTROYED ENTIRE FLE

ET"

PRINT "GOOD WORK. "

LET P=P+4+RND(3)

GO TO 99

CLS

PRINT , "SHOOT NOW"

PRINT , "=====#=«="

PRINT, , "SD"

PRINT, "##A"

PRINT, "TAAAT"

PRINT, "#G#G" , , "SD"

PRINT "SD"

INPUT W*

RETURN

P"
95

PRINT "DESTROYED SMALL GROU

LET P=P+2«-RND<2>

GO TO 99

PRINT "DESTROYED 1 SMALL CR

AFT"

LET P=P+RND<2>

PRINT "POINTS: #",P

101

INPUT W*

102

GO TO 14

Listing 2: Bonus Ship; 4K ROM, over IK RAM.

LET X=0

1 00

IF P>249 AND X»0 THEN 60 S

UB 104

104

PRINT "** BONUS SHIP **"

106

LET Z = Z + 1

1 08

LET X=l

110

RETURN di X

SYNC Magazine

8K ROM; IK RAM

Micro Invaders

Cyril B. Smith

In Micro Invaders, a space fantasy
game in Basic for the 8K ROM, IK RAM
Sinclair, the Earth is under attack by a
fleet of Micro Invaders from outer space.

You are in charge of a mobile inter-
cepter launcher defending the Earth.
Intelligence has reported that the invad-
ing ships can be destroyed only by hitting
them just inside the left landing leg. This
requires pinpoint aiming. You control
your launcher movement with the arrow
keys using 5 for left and 8 for right. You
launch your intercepters by pressing the
zero key.

Cyril B, Smith. 4737 Shadowslen Dr.. Colorado
Springs, CO 80907.

3®

4.0

4-5

100

105

4.5

110

115

120

125

130
1
135
14-0
14-5
150
155
150
165
170
175
180
200

LET G=0

LET G=G+5

LET B=15

LET N=5

LET L=0

DIM R(5>

GOTO 60

CLS

LET N=N-1

IF N=0 THEN GOTO 15

LET R=20

LET C-=0

IF L=20 THEN GOTO 200

FOR M*l TO N

LET R «H) =INT <RND*18+7> ,

NEXT M

FOR I-i TO 12

FOR M=l TO N

PRINT RT L,R<M);'-rt'*

IF R-L RND B=R(M) THEN GOTO

NEXT H

IF INKEY$="0" THEN LET C*l

IF C=l THEN GOTO 1*0

IF INKEY*='5" THEN LET B=B~

IF INKEY*="8" THEN LET B=B+

GOTO 14-5

LET R=R-2

PRINT RT fi,B;"JL' „

IF R<L THEN LET C=&

IF R<L THEN LET R=2

PRUSE 25

CLS

NEXT I

LET L=L+4-

PRINT'flT 21,20,G-N;

IN^flDE

The invaders come swooping in from
outer space in formations of five space
ships. The ships can change formation at
times, and they can hide behind each
other. Hitting one ship results in a forma-
tion rearrangement and a delay in renew-
ing the attack.

If all the ships of the formation are
destroyed before they reach you, you are
assigned a new formation to deal with.
The number of craft destroyed is shown
in the lower right of the display. The
game is over if your launcher is hit by the
invaders.

Since the program is quite full, more
memory would be needed to add anything
unless the efficiency of the program can
be improved.

Program notes:
Line 100: graphics on T and Y.
Line 145: graphics on Q and 4. H

Floppy Disc

Hi-Res Vid,

Printer

Plotter

Memory

Speech

Modem

A-D

D-A

Etc. Etc.

From over 50 manuf.

AERCO

iiiiiiiiiiiiil V ^ »*

a«©&E)G) tf^I

ZX STD BUS INTERFACE

•ONBOARD MEMORY
EXPANSION OPTION

• MEMORY-MAPPED PORTS

• PROVIDES POWER TO ZX

• ALLOWS OVER 6M CABLE

• HI -POWER BUS BUFFERS

• DELIVERY FROM STOCK
ASSM. &
TESTED

o o o o

OPTIONS:

• CONVERT ZX EDGE CON.
TO RIBBON HEADER $30

• 2K RAM EXPANSION $15

• 4K RAM EXPANSION $25

§^£

BOX 18093 AUSTIN
TX 78760-8093

(512) 385-7405

§USQ®[L&[IR

^^^

"BAC-TRAC"

16K GAME FOR ZX81 — SiMILIAR
TO PAC-MAN

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ZX-81

H you have a ZX-81 with 1K RAM you can now
have more than jgn times the program size (with
filled screen) using this new 2K RAM kit

Spending $54 90 tor a bulky module is no
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8K ROM; IK RAM

Comet
Crusher

Chuck Dawson

FLASH!!! Astronomers have spotted a
hitherto unknown comet a million kilo-
meters from the earth. Calculations indi-
cate that it will collide with the Earth's
atmosphere at a shallow angle and will
probably break up into many pieces. Each
of these pieces could destroy a city. Top
scientists have advised placing special
Comet Crusher missiles at strategic loca-
tions around the world with the hope of
blasting the comet fragments into dust
before they can hit any of the populated
areas.

Leaders of countries around the world
have issued an urgent call for volunteers
to man the Comet Crusher missile batter-
ies. Those who apply must have a keen
sense of timing and iron nerves, because
millions of people will be depending on
them. Physical strength is not required,
for one need only push the launch button
to place the missile close to the fragment
as it streaks overhead.

As a successful applicant you have been
assigned to one of the launch sites with
the following instructions:

1) Check your ZX81 computer. If it
has over IK RAM, enter the program in
Listing 1. Note the following lines:
30 graphics on 3, 8, T, 4.
50 graphics on S

1 10 leave 17 spaces inside the ** ".
140 graphics on 3, 8, T, 4. and
asterisk.

Chuck Dawson. 6320 Victoria, Fort Worth. TX
76118.

2) If your computer has IK RAM, enter
the program in Listing 2. Note the follow-
ing line:

2 graphics on D.

3) If your computer is a ZX80 with 8K
ROM, add these lines to Listing 1 :

85 PAUSE 45

86 POKE 16437,255

4) After entering your program, SAVE
it before you run it.

5) Hit SLOW and ENTER; then hit
RUN and ENTER.

6) After your viewing screen is func-
tioning, you are ready to launch your
pulverizing missiles against the assigned
fragments. To fire press F.

7) Hits are recorded and reported to
the coordinating computer to make sure
that no fragments will slip through the
world-wide network. H

Listing 1: Comet Crusher (8K ROM; over IK
RAM >.

1 REM "COMET CRUSHER 1 ' TO SflUE
GOTO 500
5 CLS

10 LET H= .

15 LET

£0 LET i^3?

25 LET X=0

50 PR I NT fiT ai.g, s ■ ' s « M ^«ii"««

60 UNPLOT X-3

70 PLOT -

ee LET <=>

90 IF r - 53 THEN GOTO 1

100 IF INKEv*= F" THEN LET ft = 1

110 IF INKEY*="F" THEN PRINT RT
20 .0. "

122 IF P-0 THFN GOTO 30

130 LET H=H-1

140 PRINT RT H . 19. " m " . TfiB 19 ; " I
'.;TRB 19;'A".TflB 19,"* ", TfiB 19

150 IF X=39 RND He 4. RND H>0 THE

J GOTO 200

160 IF H^O THEN GOTO 1

170 IF H = i7 THEN GOTO 50

180 GOTO 60

200 CLS

210 PRINT fiT 3 . 19., fijfcttM"

220 PRUSE 500

2 30 RUN

500 SfiUE "COMET CRUSHER'

5 10 RUN

Listing 2: Comet Crusher |8K ROM; IK RAM).

-PiNT fiT 20 . 19; "uumum"

LET X=0

LET fi=0

LET 1=2

LET Y=30

PLOT 4-0,2

14-

IF INKEY*="F " THEN LET fi = l

PLOT X ,Y

UNPLOT X.Y

LET X=X + 1

£5

LET Y=Y+RND*2-1

IF NOT fi THEN GOTO 14.

UNPLOT 4-0,1-2

PLOT 4.0, 1 + 1

IF X=4-0 AND Y^I-2 FIND Y<I+2

THEN GOTO 35

LET 1=1+1

GOTO 16

PRINT -fiiar '

SYNC Magazine

You are the pilot of a space ferry going
back and forth through the asteroid belt.
This calls for highly skilled navigation to
avoid hitting or being hit by the asteroids.

The asteroids are represented in your
navigation tank by the O's. and the posi-
tion of your ferry is indicated by the
asterisk. You control your movement by
the arrow keys 5 and 8.

If your ferry and an asteroid collide,
the asterisk becomes inverse. Then you
must get another ship. You build your
piloting credentials by recording how
many times you have successfully crossed
and recrossed the belt. In IK the com-
puter cannot keep the count for you.

M. Hampson. 7 Hereford Dr.. Clithcroc, Lanes
BB7 UP, U.K.

Reprinted with permission from The Ultimate

Magazine.

Listing 1.

1 REM 11111111111111111111111
1 11111 11 122£22222£2222222222222£
222222222333333333Cr3333333333333
3333 33 3334.4-4.4-4.444.4 444.4444~444-4.444
4.4444.44445555555555555555555555b
5S5S55555666666666eS66656666666K
66566666677"?7777777777777777"7?-^
777777777

IS FOR Z= 16544 TO 16736

23 INPUT X

3® PRINT <5TR$ (X+1000) ) (2 TO

8K ROM; IK RAM

43 POKE Z. X
50 NEXT Z

Listing 2.

006, ©16,
062,008,
24-5,008 ,
014,016,
062,008,
245,008,
254 ,255,
071,035.
008,062,
503,071,
079,040,
120, 119,
032,002,
203,206.
134,254.
205, 245 .

064,060,
008,042.
200,054.
032,004
032,009.
013,000
205,245,
064,

197,
215,
062
197
215
062
032
126

000

040
002.
035
203
120
015
008
169
079
014
000
013
012
000
008

014 ,

193 ,

008.

006,

193,

008.

230

079

215,

002.

013,

121.

142,

254.

032

062

194

006

064

058

032

062

121

062

000

197
215

000

197
215
033
197
225
005
013
119
254
001
002
052
215
008
126
037
001
016
061
023

205,
014,
193
205
006
193
, 130,
229
193
005.
012,
,035
015
.032
.203
,215
.064
197
,254
.064
.012

185

,050
,215

245
016
016
24S
016
013
064
205
035
004
043
254
032
002
198
225
058
205
052
254
254
032
033
195

,008
,205
,234
,008
,205
, 121
, 126
,24 5
, 126
,203
,043
,001
,002
,203
, 229
.035
,033
,245
, 193
,247
,239
,001
,064
,212

I i st inn 3.

8 RRND

9 PRST

10 FOR Z=NOT PI TO URL
EP URL "3"

20 POKE URL
*URL "3" J +URL

21 POKE URL
*URL "8"> +URL

22 POKE URL
*URL •■4-")

30 NEXT Z

4.0 POKE URL

45 SLOW

60 PRINT **B"

70 RRND RND**RND**RND

27" ST

165 14 "+Z, INT (RND

16515" +Z, INT (RNP

16S16"+2,INT IRND

15417" ,NOT PI

'16544."

Crossing the Asteroid Belt

M. Hampson

The directions are as follows:

1 ) Do not use your RAM pack.

2) Enter the program in Listing 1. Be
sure to type in line 1 as listed.

3) Type in RUN and ENTER.

4) Enter all the values in Listing 2. Be
very careful. About halfway through the
list, the ZX81 will run out of memory.
Type CONT(inue) and continue entering
the numbers.

5) Delete all the lines in Listing 1 except
line 1 by entering the line number follow-
ed by ENTER.

6) Enter the lines in Figure 3. Note: the
graphic in line 60 is an inverse asterisk
(on B).

7) Type in RUN and ENTER and your
journey across the asteroid belt begins. V

zxchess

it's the best!

IS HER[ !!! ]t is the fastest, most versati
' 81/16K {or IX 80/16K with 8K ROM).

f Chess proqra* *

levels of play (up to si. levels of " 1 ook ahead" * ) and its
tandard Chess »oves (including CASHING and EN

PASSANT. »4Kfs ZXCHESS II a challenge for both beginners and advanced players.

Choose your le-e! of play, choose to play Black cr Nhite at any stage of the
ga«e - you can even set up the board to txaainc any special position' for
beginners. ?XCH£S! . even suggest noves for you if you are stuck 1

fl trL ••• that plays a g'cat gaie of Chess" Available for only

$?4.Sd (plus $1 post and packing charge) fro* the following distributors:

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N Hill Station Toronto MS* 3Y7 Buffalo

Ne- fork k.Y. 10156 Canada N.Y. K?03

July/August 1982

8K ROM; IK RAM ; 16K RAM

DEF on the Sinclair

Jon Passler

Occasionally a program listing such as
"3-D Plot" from Creative Computing's Basic
Computer Games contains the DEFine
statement which allows the programmer
to define a function in the form

DEF FNA(X)=(expression)
FNA merely stands for FuNction A." and
the variable X in the parentheses following
FNA is termed the "dummy argument."
Usually the expression to the right of the
equals sign in the DEFine statement has
at least one X in it. Of course, variable
names other than A and X could be used.
A simple example would be the state-
ment

DEFFNA(X) = X**2+X
Normally, when FNA is "called" or used
within the program flow, an argument is
given within the parentheses different from
the dummy argument, but which replaces
all occurrences of the dummy argument
in the DEFine statement. FNA(2) would
have the value of 2**2+2. or 6. while
FNA(A + B) would be the result of
(A + B)**2+A+B. FNA can be treated
like any other numeric variable. The only
difference is that it is the result of an
expression DEFined at the start of the
program, outside the program flow, and
the programmer can alter the argument
of the expression.

Jon Pussier, 344 Cabot St., Beverly, MA 01915.
64

The definition could have contained
more than one dummy argument or vari-
ables which are not dummy arguments,
such as

FNB(F t G)=F*G-Q/R
Functions can also be used as arguments
for other functions, for example

FNB(3,FNA(A + B))
would be the result of
3*((A + B)**2+A + B)-Q R
The DEFine statement is useful to simplify
equations or cut down on programming
where one equation is used at several
points within the program.

One way around DEFine in Sinclair
Basic is to replace all FN calls with the
expression in the definition. This often
requires breaking down an equation to
simplify it.

Another is to use the 8K VALue function
which can evaluate a string such as "2" oi

"2+2" or even "X**2+X". The solution
then is to replace DEF FNA with

LET A$=( expression)
and replace the FN call with VAL A$.
The only problem appears when something
like FNA(A+B) appears. We cannot call
the function and define the argument all
in one statement. Generally, if several
different arguments are used in the FN
calls, it is best to set the dummy argument
equal to the argument before calling for
VAL AS. setting, for example, X = A + B.
Listing 1 is the program for "3-D Plot"
from Basic Computer Games. Here
FNA(Z) is defined in line 100 as

30*EXP(-Z*Z 100)
and in line 150 the argument is

SQR<X*X + Y*Y)
which replaces all Zs in FNA. Line 150
also sets Z, which is not related to the Z

I.isiinu 1: 3-D Plot, Original Program. _

100 DEF FNA (Z)=30*EXP(-Z* 3/100)

110 FOR X=-30 TO 30 STEP 1.5

120 L=0

130 Yl=5*lNT(SQR(900-X*X)/5)

140 FOR Y=Y1 TO -Yl STEP -5

150 Z-INT<25+FNA(SQR(X*X+Y*Y) )-.7*Y)

160 IF Z<=L THEN 190

170 L=Z

180 PRINT TAB( Z); M *"

190 NEXT Y

200 PRINT

210 NEXT X

SYNC Magazine

Get the most from your SINCLAIR

with these practical, program-filled books from Sync\

Getting
Acquainted
With Your

ryvoi «JAOI and

ZX81 zx80

More than 70 Progr*

TheZX81
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The

Gateway
Guide to the

* Real Time Graphics
» Information Processing

• Educational Applicat

• Monitor Listing

Second Edition
More than 80 Programs

The ZX81 Companion

by Bob Maunder

The ZX81 Companion follows the same
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Companion, and assists the ZX81 user
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information retrieval, education and
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scores of fully documented short rou-
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Monitor. "Thoughtfully written, detailed,
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5 1 /2"x8",132 pages. #17P$8.95 ($2.00)

Getting Acquainted With
YourZX81

by Tim Hartnell

This informative volume for the new
ZX81 user contains more than 70 pro-
grams to help the reader get the most
from his Sinclair computer. Game
programs include Checkers, Alien
Imploders, Blastermind, Moon Lander,
Breakout, Star Burst and Derby Day. The
book also shows programs for cascad-
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tables, data sorting, equation solving,
plus the use of PLOT SCROLL, PRINT
TAB, PEEK, POKE and much more!
5V2" x 8", 120 pages. #15Y $8.95 ($2.00)

The Gateway Guide to the
ZX81andZX80

by Mark Charlton

The Gateway Guide is a practical pro-
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furnishes over 70 fully documented pro-
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have been written for easy conversion
from machine to machine (ZX81, 4K
ZX80 or 1 K ZX80). The Gateway Guide
describes each function and statement,
illustrates it with a demonstration rou-
tine or program, and combines it with
previously discussed material to help
you understand vour computer
5 1 / 2 " x8",172 pages. #160 $8.95 ($2.00)

Computers for Kids (Sinclair Edition) by Sally Larsen

This new edition of Computers for Kids is written specifically to introduce
children aged 8 to 13 to the ZX81. The book requires no previous knowl-
edge of algebra, variables or computers, and it enables a youngster to
program a ZX81 in less than an hour. There's also a section for parents
and teachers. "Computers for Kids is the best material available for
introducing students to their new computer."

—Donald T Piele, Professor of Mathematics,
University of Wisconsin-Parkside.
8Y2" x 11", 56 pages. #12S $3.95 ($1.00)

All volumes are softbound.

Creative Computing Press, Dept. Z720 , 39 East Hanover Ave., Morris Plains, NJ 07950

Please send books listed below:

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CHARGE ORDERS— For Your Convenience PHONE
TOLL FREE 800-631-8112, In N.J. Only (201) 540-0445.

Listing 2: 3-D Plot for Sinclair (8K ROM. IK
RAMI

in FNA(Z), to an integer value using the
FNA call. This program is translated into
Sinclair Basic <8K ROM, IK RAM) in
Listing 2. Here the string variable AS is
used to replace DEFine and set the
argument equal to

SQR(X*X + Y*Y)
in line 145 before calling for VAL AS. AS
is an input since several different functions
are plotted. The same results could be
obtained by adding

146 LET A=30*EXP(-Z*Z/100)
and changing VAL AS to A in line 150,
except that line 146 would have to be
edited each time the function is changed.
The functions are slightly altered to
run on either IK or 16K RAM. Neither
program, however, will work correctly
with defective 8K ROMs. The plots appear
within a circular X-Y plane tilted about
30 degrees toward the viewer with the
cuive rising above or falling below the
plane.

Try the following functions with the
IK program:

20*EXP(-Z*Z/100)

20*SIN(Z/10)-15

SQR ABS(150-Z*Z)*.4-2

2()*(COS(Z. 16))-5

20-20*SIN(Z/18)
In the 16K version all the five functions
above are held in F$ (see Listing 3). Each
function word such as SIN uses only one
byte in FS. At line 180 a zero is POKEd
into DF-SZ, which is the system variable
with the number of lines (usually two) in
the lower part of the screen. Entering a
zero into it allows printing the function
on rhe 24th line. An input cursor will
crash the system if called for when there
is no room for it; so lines 330-340 replace
a dummy input to stop the program
temporarily (press any key to continue).
This is a rather unusual example of an
occasion when using a string variable to
hold a function or functions can be useful.
The technique would also be useful where
a function is used several times within a
program to facilitate the translation of a
DEFine statement or to highlight a function
at the start of a program.

To use the programs, enter Listing 2,
press RUN and NEWLINE and then enter
one of the five functions above and observe
the results. If you have 16K, enter the
expanded version in Listing 3, press RUN
and NEWLINE. However, since the func-
tions are already included in the program,
you do not have to enter them again. V

10S INPUT H*

120 LET L=*

130 LET Y1=5#INT ISOR (408-X*X)

14-0 FOR Y=Y1 TO -Y 1 STEP -5

14.5 LET Z=SOR tX*X+Y*Y)

150 LET Z = INT (25+URL fi$-.7*Y>

160 IF Z<=L THEN GOTO 190

170 LET L=Z

190 NEXT Y

210 NEXT X

Listing 3] 3-D Plot for Sinclair (8K ROM, 16K-
RAM)

100

110
1 20

130

L50

REM 3-D PLOT
DIM F* (5.. 16)
LET F4 (1) ="25*EXP (-Z*Z^10G

LET F$(2) ="25*5IN (Z, 10) -15

LET F* (3) ="25* (COS CZ/iS) ) -

LET P$(4)="25-25*5IN (Z/18)

160

LET F* (5> ="25*EXP (-COS (Z/

6 * ) -

-13"

170

FOR 6=1 TO 5

130

POKE 164 18,0

1-90

PRINT RT £

20©

PRU5E 99

210

FOR X=-25 TO 25

22©

LET L=0

230

LET Y 1=4.* INT (SOR i625-X*X>

4-)

240

FOR Y=Y1 TO -Yl 5TEP -4

2S0

LET Z = S G R f X * X * r * Y 3

260

Z = INT ~5+UPL F$(B) -.7*

270

IF Z<=L THEN GOTO 310

280

LET L=Z

290

P L OT X + 38 , 2 - 8

300

PRUSE

310

NEXT V

320

NEXT X

330

PRUSE 9999

34-0

IF INKEY$="" THEN GOTO 330

350

CL5

360

NEXT B

370

STOP

SYNC Magazine

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*A 4K Star Atlas as the moving

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*9-each fuel and skill levels that

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*4 ways to lose — no fuel, no oxygen,

no gun power, or no shields. 1 way

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*An enemy data generator imbedded in

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4K ROM <8K ROM); IK RAM

Handling Strings from
Another

Ken Berggren

Does this story sound familiar? One day.
Fred found an excellent short program in
a magazine article and he decided to
translate it for his ZX80. But after entering
only a few lines of the program, he ran
into a statement like this:

250DIMNS(4)
'What in the world Hoes that mean? he
asked himself. When he could not answer
that, he consulted a friend with a TRS-80.
His friend explained that it works just like
a regular DIM statement but with strings
instead of numeric variables. That is, DIM
N$(4) sets up four strings with the same
name. NS, but individually numbered 1-4.
Fred frantically flipped through the pages
of the ZX80 manual and found the terse
explanation of the DIM statement on page
89. But there was nothing there about strings.
So, he set aside the magazine article and
decided to stick with programs written
just for the ZX80.

Well, if Fred sounds like some people
you know, then consider this article dedi-
cated to them. SYNC is a fine magazine,
but it cannot publish every program that
will work in the ZX80. And just because
you cannot use a statement like DIM N$(4)
does not mean that you cannot translate a
program that uses it.

Now you 8K ROMers realize that your
supercharged machines will DIMension
strings without any hocus-POKEus. and
you may be tempted to turn the page on
me. But stick with me because I think that
you will find this technique very interesting
if not useful. Any way , from now on we will
be talking strictly in terms of the 4K ROM.

It is true that the people who designed
the 4K ROM left out the ability to DIMen-
sion strings. However, with a few well-
placed POKEs, you can plug up that hole
in the 4K ROM.

Ken Berggren, 104 Ridgeway Ave.. Louisville. KV
40207.

For example, enter this short program.

100 FOR 1 = 1 TO 4
110 POKE 16450.1 + 37
120 INPUT AS
130 NEXT I

The A in line 120 is stored in the memory
location 16450. The code for an A is 38,
So. at present, a 38 is stored at the location
16450. When you RUN this program, it
will execute lines 1 10 and 120 four times.
The first time through, line 1 10 will POKE
a 38 ( 1 +37) into the location 16450. Then,
line 120 will INPUT AS. But the second
time through, line 110 will POKE a 39
(2+37) into location 16450. Since 39 is the
code for a B, line 120 will then INPUT BS.
This program actually changed itself! The
third time through the loop, line 1 10 POKEs
a 40(3+37) into the memory location, and
line 120will INPUTCS. When the program
is finished, it will have stored four strings:
AS, BS. CS. and DS. You can imagine that
these are numbered 1-4 because when 1 = 1
vou INPUT AS and when I =4 you INPUT
D$.

RUN the program and enter four words.
Now change line 120 to 120 PRINT A$
and then GO TO 100. The method will
work with INPUT, PRINT or any other
string functions.

Some of you may thinking, "Big deal.
What good is all this?" I think that the
following two programs will illustrate the
virtues of this technique.

The first program is a simple sort program.
We all know that computers are very good
at putting numbers in order. And since
computers store letters as numbers, they
are also good at putting words in order
(alphabetical order, that is). The program
will alphabetize up to 25 words and will
display up to 22 of them.

Using the program is simple. Just enter
the number of words you want to alpha-
betize and then enter the word with a
NEWLINE after each one. When you have
had the last word, the program takes over,
and, a few seconds later, the words are
displayed in alphabetical order.

I think that it is worth noting line 240. 1
do not know if other Basics let you use
inequalities with strings, but ZX80 Basic
does. That is a very nice feature. If you
want to put the words in reverse order,
simply reverse the inequality.

This program is not so great by itself.
But it could be developed into a good
utility program for handling a list of the
names of friends for an address book or
names of students for a grade book. It
could possibly be adapted to help teach
dictionary skills.

The second program illustrates the
technique by computerizing a card game
played something like Rack-0 (by Milton
Bradley). The POKEing is used to call
each player by his name rather than the
impersonal PLAYER 1. PLAYER 2, etc.

In this game, the players are dealt ten
numbered cards. The remaining cards are
placed face down, and the top card is
turned face up to form a discard pile as in
Gin. The object is to get ten cards in
numerical order (not necessarily consecu-
tive order). This is done by drawing a card
from either pile and exchanging it for one
of your cards.

In this version, of course, the computer
handles all the cards. First, it shuffles them
and places them into each player's "rack."
Then the first player's cards are displayed
and he is asked if he wants the card showing
in the discard pile. If he does not. he enters
"NO," and he is given a card from the face
down pile. If he does not want that card,
he enters "NO" again and his turn is over.
If he decides to take either card, he enters
"YES" and the computer will ask where in
his "rack" he wants the card to go. The
player then enters a number 0-9. His card
will be placed in that position, and his turn
will end.

At the end of each player's turn, the
computer will display the cards that the
player has in order so far. Then a NEWLINE
will start the next player's turn.

The game ends when one player get his
cards in order. To start a new game you
have to RUN the program again.

If you have more than IK of RAM, you
could probably teach the computer how
to play the game and then play against it.
You could also allow more than four players.
But be careful. Any modifications of these
programs may affect the POKE locations.
To make sure, LET 1=0 and then GO TO
the POKE statement in question. If the
next statement does not contain a 9$ after
you do that, you will have to change the
POKE location until it does. But trial and
error will not work very well if you make
big changes or if you write your own
programs. Then you will need a more exact
method of finding the location of a specific
byte in a program.

SYNC Magazine

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.Program I. Alphabetize |4K ROM; IK RAM)..

Program 2: Card Strings (4K ROM; IK RAM)_

One way is to count the bytes in each
line and add them up. Every line has two
bytes for the line number (no matter how
many digits), one byte for the Newline at
the end of the line, and one byte for every
keystoke in between. So, in the example
program, line 100 takes 9 bytes, line 110
takes 14 bytes, and line 120 takes 3 bytes
up to the A for a total of 26 bytes. Add 26
to 16424, which is the starting address of
every 4K ROM program, and you get 16450.
That is the actual location of the A in
memory. However, counting all the bytes
in a long program is a very tedious chore. 1
found a better way.

When USR(24) is put into a program, it
stops the execution of the program and
returns the starting address of the next
line. To illustrate, insert 115 PRINT USR(24)
into the short program and then GO TO
1 15. 16458 appears on the screen because
that is now the starting location of line
1 20. Line 1 1 5 takes 1 1 bytes so. when it is
deleted, line 120 will move up 1 1 bytes to
16447. Adding the three bytes of line 120
again shows that the location of the A is
16450. USRI24) is an invaluable utility
whenever you need to know the location
of a byte in your program.

A lot of programs out there in books
and magazines can be adapted to the ZX80.
But sometimes you really have to work to
get them to. Now the lack of DIMensioned
strings is no longer a problem. There are
other shortcomings in the 4K ROM in
dealing with other Basics. Yet, with a little
determination and ingenuity, you can
usually get around them.

1 00

PRINT "HOW MANY ENTRIES

110

INPUT N

120

F0RI=1 TO N

1 30

PUKE 16478, I

140

INPUT **

I 50

NEXT I

200

FOR 1=1 10 N

210

FOR J=l TO N-I

220

POKE 16537, J +37

230

POKE 16540, J +38

240

IF B*>C» THEN GO SUB 90

250

NEXT J

260

NEXT I

300

FOR 1=1 TO H

5 1

POKE 16584, 1+37

320

PRINT D*

330

NEXT I

340

STOP

900

POKE 16658, J +37

9 1

POKE 16664, J +37

920

POKE 16667, J +38

930

POKE 16673, J +38

940

LET ZS=E*

950

LET F*=G*

960

LET H*=Z*

970

RETURN

Notes:

100-150: Get the words.
130: Changes A$.
200-260: Sort the words.
770- Chanoe<; RS
230: Changes C$.
300-340: Display the words.
310: Changes D$.
900: Changes ES.
910: Changes F$.
920: Changes GS.
930: Changes HS.
900-970: Move the words.

. Sample Run _

100 PRINT "PLAYERS (2-4) ?"

110 INPUT N

120 FOR 1=1 TO N

130 PRINT "PLAYER**"; I

140 POKE 16489, 1+37

150 INPUT A*

160 NEXT I

190 LET E=20+10*N

200 DIM CCE)

210 FOR 1=1 TO E

220 LET P=RND<E>

IF C(P)>0 THEN GO TO 220
240 LET C<P)=I
250 NEXT I
300 LET F-E-19
400 FOR 1=1 TO N
410 CLB
415 LET T=0
420 POKE 16616, I
430 PRINT B*
435 PR INI
440 FOR J="-0 TO 9
450 PRINT J;

452 FOR L=0 TO C(J*N+I)/N/4
454 PRINT "#";
456 NEXT L
458 PRINT C(J*N+I)
460 IF T=0 THEN GO TO 490
465 IF I >9 THEN GO TO BOO
470 I F C ( J*N+ 1 ) ■■ C < J ^M+N+ I ) T HEN

RE I URN
480 LET l=T+l
490 NEX I J
495 PRINT
500 LET Y*="SH0W"
5 1 PR I NT Y* ; " **CARD= " ; C ( P > ; " #1 A

KE
520 INPUT Z*

530 IF Z*>"X" THEN BQ TO 600
540 IF Y$=" DRAWN" THEN GO TO 65

550 LET P=P+1

560 IF P-E THEN LEI F-E-19
570 LET Y*= N DRAWN"
580 GO TO 510
600 PRINT "PLACE "
610 INPUT J
620 LET T=C(J*N+1)
630 LET C(J»M+I>=C<P)
640 LET C(P)«T
650 CLS
660 LET f=l
670 GO BUB 430
680 INPUT 1%
700 NEXT I
710 GO TO 4
800 POKE 16988, H
310 PRINT CS>; ,! **WINS"

Notes:

100-160: Get the players.
190: E= total number of cards.
200-250: Shuffle the cards.
300: P— pointer to show card.
410-490: Display a player's cards.
452-458: Spaces each card over by magni-
tude.

465-480: Part of winner test subroutine.
500-580: Players pick their cards.
600-640: Chosen card put in "rack."
650-680: Test for winner.

Display cards in order so far.
700: Next player's turn.
710: Back to player 1.
800-810: Print the winner.

SYNC Magazine

NK ROM Versions

Although the article is intended to help
4K ROM users, we thought the 8K ROM
users might like to use the programs so
the 8K ROM Versions are also given below
in Programs 3 and 4. ^

_Pro R ram 3: Alphabetize |8K ROM; IK RAM)..

100 PRINT "HOU MflWY ENTRIES?"

110 INPU1

115 £>IH R*tN

130 FOR 1=1 TO N

14-0 INPUT ft* (1.1

150 NEXT I

200 FOR II TO N

210 FOR .

24-0 IF H$ i <J) >R$ U + l; THEN GOSUB

900

250 NEXT J

260 NEXT I

300 FOR 1=1 TO N

320 PRINT h$ ( I)

330 NEXT I

340 STOP

94-0 LET 2*=fl»lwO

950 LET fl*tJ» =R*iJ+l)

960 LET H$ CJ + JL) =Z*

970 RETURN

Program 4:
Card Strings (8K ROM; over IK RAM).

100 PRINT "PLflYER5(2-4l^"

110 INPUT N

115 DIM R*(N,10)

120 FOR 1=1 TO N

130 PRINT "PLAYER " ; I

150 INPUT R*(I>

160 NEXT I

190 LET E=20a0*N

200 DIM C <E)

210 FOR 1=1 TO E

220 LET P=INT (RND*E) +1

230 IF C (P) >0 THEN GOTO 220

24.0 LET C (P> =1

260 NEXT I

300 LET P=E-19

4.00 FOR 1=1 TO N

4 10 CLS

4-15 LET T=0

430 PRINT R$(I)

435 PRINT

440 FOR J=0 TO 9

4 50 PRINT U.;

4-S2 FOR L=0 TO C(U*N+I)/N/4

454 PRINT " ";

456 NEXT L

4-53 PRINT C(U*N + I)

460 IF T=0 THEN GOTO 490

465 IF T>9 THEN GOTO 800

470 IF C ( J*N+I) >C <J*N+N+I> THEN

RETURN

4 80 LET T=T+1

4 90 NEXT J
495 PRINT

500 LET Y$="5HOU"

510 print Y*; •■ CRM>«"; C (P) ; " tr

KE? M
520 INPUT Z*

530 IF Z$>"X" THEN GOTO 600
540 XF V*=*DRRWN" THEN GOTO 650
550 LET P=P*I

560 IF P>E THEN LET P=E-19
570 LET Y$ = "DRflUIN"
580 GOTO 510
500 PRINT "PLRCE^"'
610 INPUT <J
620 LET T=CtO*N+I>
6 30 LET C(JtN+I)sCIP)
640 LET C (P) =T
650 CLS
660 LET T=l
570 GOSUB 430
680 INPUT Z$
^00 NEXT I
"10 GOTO 400

5 10 PRINT R* I I

CYBORCWc^RS

BUT A COMPLEX SIMULATION OF FOUR MILITARY- INDUSTRIAL
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ONE TO FOUR PLAYERS COMPETE WITH EACH OTHER AND OR
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ORDER FORM FOR CyBOOTO

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scratch. The program can be run at the end of each step and will take shape as the kit
steps are completed. These kits are made for a minimum system of the ZX80 with 1 k
of memory and include translation for ZX8 1 s as well as guidance for going further.

Our aim is to provide the personal joy of programming as well as the fun of playing
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PRISONER - Cooperate or trick your
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July/August 1982

SINCLAIR ZX81 & TS1000 SOFTWARE
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4 8K, IK BASIC Programs - Sketchpad.

Combinations of 7, Enterprise (picture

only) and Hebrew Tutor, $10.00.

Reply To

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' ZX81 KEYBOARD TACTILE FEEDBACK '
FEEL WHERE YOUR KEYS ARE*

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8K ROM: 16K RAM

The 8K ROM and 16K RAM have
given ZX80/81 users new possibilities in
programming their own games. Alien
Treasure is an example of how some of
these new capabilities may be used.

In Alien Treasure two kinds of treasure
are scattered over the surface of a planet
far from earth. Your ship has landed, and
you have sent out your robot searcher
which you guide from your control room.
The field of search shows on your ZX81
as a full screen display. The treasure is
marked by inverse video periods which
are worth one point each and by inverse
video asterisks which are worth 10 points
each. (You can set the vaiues in your own
currency if you wish.) However, there are
always hazards in searching for treasure.
In this case a powerful monster is guard-
ing the search area. While your robot is
attempting to pick up the treasures, you
must guide it to avoid this monster which
appears on your screen as an inverse
video 0. Your robot, shown as a graphic
square, is moved about by the use of the
cursor control keys 5, 6, 7, and 8. The
robot also can take a jump away to a
random position in the same column by
using the key. However, you must use
this key with caution because the robot
may land right on top of the monster.

The current total of your successful
treasure gathering is displayed on the
screen in the upper left corner. The total
you must beat is displayed to the right of
yours.

The game uses a 22 * 32 array to keep
track of the treasure locations. When the
game is run, it takes about 20 seconds for
the screen and the array to be set up and
loaded with the proper values. So do not
hit the BREAK key too soon because you
think the program is in an infinite loop.

Before you SAVE this program, exe-
cute the CLEAR command. Otherwise
you will save the entire array along with
the program, and it will take much longer
to SAVE and LOAD in the future.

Alien Treasure has proved to be an
interesting and challenging game for those

Gary G. Chandler. ATU Box 283, Russellvilie,

AR 72801.

Chandler £

who have tried it so get out your keyboard
and start the search.
Line notes:

30: inverse space

36: inverse asterisk

44: inverse period

65: inverse zero

66: inverse graphics on A

73: inverse letters in "' ,

85: inverse space

89: inverse space %

1 LET Cl-0

2 REM TRER5URE CHRSE

4. REM BY GRRY G. CHftNDLER

5 LET X=®

6 LET Y = 16

7 LET Y1=Y

8 LET X1 = X

9 LET R = INT (RND*22)
13 LET B=*INT (RND*32)
12 LET C=*0

20 DIM HC22,32)

26 FOR 1=0 TO 21

26 FOR d=0 TO 31

30 PRINT RT I,U;"*"

31 IF 1=0 OR U=0 THEN GOTO 50

36 PRINT RT I,J;"H"

4-0 IF NOT RND<.1 THEN GOTO 50

4.2 LET H (1+1, J + l) =1

4.4 PRINT RT I,J;"|"

50 NEXT J

60 NEXT I

65 PRINT RT X,Y, "H"

66 PRINT RT R^B;"!"

67 IF H (R + 1..B + 1) =2 THEN LET C«
C+10

68 IF H(Rfi,Bfl)=2 THEN LET H<
R+1,B+1) =0

69 IF HIR+1,B+1>=1 THEN LET C=

" + 70 IF H (R+l .B+l) =1 THEN LET H<
R+1,B+1> =0

72 IF OC1 THEN L ET C 1=C

^INT RT 0,0, "HI" ; C ; RT ,
' ;RT 0,21,01

R>X THEN LET Xl*Xtl
R<X THEN LET X1=X-1
B>Y THEN LET Y1=Y+1
B<Y THEN LET Y1=Y-1
" RT X,Y; "■"
=X1

8
81

82
83
84-

IF
IF
IF
IF

85 PRINT

86 LET X=

87 LET Y=Y1

88 IF X=R RND Y=B THEN GOTO 20

89 IF NOT INKEY*='"
RT fl.B, "U"
95 IF INKEY$="0
T <RND*22>

98 IF INKEY$="5

THEN PRINT
THEN LET R=IN
THEN LET B»B-

100 IF
L
110 IF

INKEY*="8"
XNKEY *-'**"

THEN LET B*B +
THEN LET fl=R+

120 IF INKEY*="7" THEN LET fi = R-

132 IF R>21 THEN LET R=21

133 IF R<1 THEN LET R-l

134 IF B>31 THEN LET B*31

135 IF B<0 THEN LET B=0

140 IF X«R RND Y*B THEN GOTO 20

160 GOTO 65

200 PRINT RT 10,10; "*#GOT YOU**

202 PRINT RT fi,Br**X"

205 PRINT RT 20,2;" PLRY RGRIN

INPUT Y OR N "

207 INPUT G*

208 IF Gt«"N" THEN STOP
210 GOTO 5

SYNC Magazine

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Fastens to ZX81

Improved Model:
Bare Board $40*

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Kit $70*

6 connectors. 9 chips, sockets

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All lines from

computer port

are on bus & in

same order

Buffered Data,

Control & Address

lines Data bus

is two-way

Two types of

connectors

9 chips needed.
. if ts are
standard.

Finest quality board

Plated thru holes

solder mask legend

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MORE Plans. Kits.
Programs Inquire.

ontinuum

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Ed. -A WORD OF CAUTION: Any
hardware project for your computer must

be approached with extreme caution.
SYNC cannot be responsible for any
problem that may arise from attempting
hardware projects. Obviously, any dam-
age to your computer can be costly in
time and mom

narcluuarE tips

Thick Black Bars

George R. Ingle

In SYNC 1:6 Cecil Bridges points out
that the thick black bars on the display
may be caused by a failing capacitor in
the power supply. However, it is not
necessary to crack open the mains power
adapter to replace the lOOOuF capacitor.
A simpler solution is to add another
capacitor, rated 20O470uFat 25wv, across
the +5v and ground connection to the
UHF/VHF modulator. This not only
corrects the leaking capacitor problem
but also greatly reduces the "lining" of
the display caused by the ZX80 display
circuit itself. Obviously, a miniature
capacitor should be used because of the
minimal free space inside the computer
case.

Comp.

Video

VHF/UHF

Modulator

*. -a

— H

200-4

« 1

70uF T

Insufficient
Filtering Solved

Robert D. Hartung

Like many others I found that the DC
filtering capacitance of the power supply
included with the 16K RAM pack is
borderline in supporting the demands of
both the RAM pack and the ZX80 with
its 17 extra ICs as compared with the
ZX81. The symptoms of insufficient fil-
tering include false LOADs from the
excessive 60 Hz ripple in the DC and a
horizontal line or blank bar moving verti-
cally through the TV display every two
seconds. If these symptoms disappear
when the RAM pack is disconnected,
either some component is drawing exces-
sive current or. more likely, the added
load of the RAM pack is causing inade-
quate filtering of the unregulated DC
power to the computer.

Memory Expansion Power Supply

George R. Ingle

David Sommers mentions (SYNC 1:6)
the problem of using an additional power
supply with his memory expansion. For
those building an additional memory
expansion unit, the following suggestions
might be helpful.

1) Insure that all components are using
a common ground return.

2) Do not connect the +5v regulated
voltages or +9 to +12 unregulated volt-
age in parallel. Instead, use a common
ground whether earth or floating.

depending on the design, and feed the
additional memory unit with a separate
+ 5v regulated supply.

3) Insure that the additional power
supply is well-filtered and uses, if possible,
a three prong grounded outlet and AC
supply cord.

(Ed. —A schematic of the authors power
supply that provides for +/5v reg., +I2v
reg., +5v reg., and -I2v unreg. is available
from the author for $1.00 and a SASEj

George R. In^le. 24593 1 2 Monterey Ave. San Bernadino, CA 92410.
74

Adding a 2200uF 50VDC capacitor
across the output wires near the power
jack eliminates the problem. Use a VOM
or an LED tester to determine which is
the positive output wire and which is the
negative in order to be sure that you are
observing the proper polarity in con-
necting the capacitor. This capacitor also
gives some protection against momentary
drop-outs occurring on the main power
lines.

A note of caution: since a capacitor of
this size stores considerable energy even
after the power pack is unplugged from
the AC outlet, I strongly recommend
inserting a small lever type microswitch
(e.g.. Radio Shack 275-016) in one of the
DC wires near the computer power plug.
This will avoid possible burning or fusing
of the power jack outlets when the plug is
inserted or withdrawn when the capacitor
is charged. The switch gives a bonus of
being a "panic" switch to get out of
endless program sequences as well as to
cut the power off when connecting or
disconnecting the 16K RAM pack.

To install the switch, cut and strip one
of the power cord wires as near to the
computer plug as practicable. Solder one
wire end to the C lug of the switch and
the other to the NC lug (normally closed).
An LED pilot light can be added at the
same time. Strip, but do not cut, one-half
inch of the other power cord wire. Again,
determine the polarity of this wire with
the wire which goes from the switch lug
to the computer plug. Solder the LED
lead which is nearest the flatted side of
the LED base (cathode) to the negative
wire. Solder a IK resistor to the other
LED lead and in series to the wire which
is positive. Carefully tape all bare leads
and connections to isolate them from
each other. Since only 45 grams of pres-
sure will open the switch, taping it to the
power cord and plug will give all the
necessary support.

Robert D. Hartung. PO Box 125. Palmvra. NY
14522.

SYNC Magazine

USE OUR PLANS AND SAVE $$$$$

SYN
SYIV
SYN

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KEYBOARD how to add a full-size keyboard
to a ZX/80 or 81. Includes instructions on how
to use any extra keys for Shift Lock, Automatic
shift. Automatic Repeat, and Reset. $5.00

POWER SUPPLY Running a little hot? Design
and build your own supply to fit your needs
at a fraction of wired price. Includes how to
estimate both present and future needs and
covers both single and multi-voltage. $5.00

BUSS Inexpensive exspansion system unlimits
your edge connector. $3.50

JOYSTICK Add popular Atari joysticks and
find out how much fun games can be. $2.50

Send check or money order to:

SYNCHRONIZE

Box 1667

Kerrville, Texas 78028

PRACTICAL ZX-8U SOFTWARE

ZX-81™ Not Just

For Games

Anymore!

ZX-PANDE <":*), LTD., an American c ■?■ , ises the tremen-

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easy-to-r* bed instructions, SIC to

allow tailoring to your special needs. Send a STAMPED 3ELF-
ADDRESSED ENVELOPE for details on these and other p rogra ms.

1. YOUR SPECIAL DAY— IK— Good example of usfflg 1
successive equations to answer a practical question.
Enter any_ date in history, and ZX-31^ will tell you the
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2. CLOCKS AND TIMERS— IK— A digital clock; stan-
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3. ANTP03JT PLOTTER— IK— Crunches any data to
allow graphing any positive data points: stock prices,
temperature, experimental data, etc. . . . ONLY $3.7<£

u. CHECKBOOK, INCOME TAX AND BUDGET QRGAL'IZER^loK
A powerful yet easy to use finance program — 10 jobs in menu
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under desired categories for budget planning and income tax
preparation. Hakes checkbook balancing easy. Ninety trans-
actions manipulated at one time with 16K. • . . 0NLT $13.75*

ZX-PANDINCLTD.
P.O. BOX 25
S'EWTON, NC 28658
704-464-2742

*ALL orders please add $1.25
to total order to cover POST-
AGE AND HANDLING. (Foreign
orders add $2.00 to cover air
costs. Your payment must be
in a U. S. dollar draft pay-
able to U. S. bank.)

Sinclair ® Computer Owners

YOU NEED THIS!

* Protects against power line glitches

* Provides extra power for add-ons

* Cuts heat in the internal rpgulatnr

The HL-1205 uses the same modern switching regulator technology
as used on big computers to trade harmful heat for extra power
so ... Just plug your ZX81 A.C. Adapter into the HL-1205, plug
the HL 1205 into the computer and turn on the switch. Add a
rechargable 12 volt battery (not supplied) to have an UNINTER-
RUPTABLE POWER SUPPLY, or operate from 12V car or truck
system A MUST FOR SERIOUS COMPUTER USERS

$35.95 plus $4.00

shipping and handling
30 day money back guarantee

To order send check to:
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HURRICANE, UTAH 84737
[8011635-2003

MUSIC and KALEIDOSCOPES

VIRTUOSO. A music synthesis program for the
Timex/Sinclair and ZX81 with 2K or more. NO
MUSIC KNOWLEDGE NECESSARY! 96 notes.
range from put put to above treble clef, any tempo.
Whole to 32nd notes. Songs may be saved for
future use. Required hardware? - - Your cassette
recorder. $6.95 pp.

PLAYER 2X81. A less versatile music program for
1K memory. Music instruction not included. $6.95
pp.

SQUARES and CROSSES, Kaleidoscopic
simulations for the same machines. IK or more.
$6.95 pp.

All on standard cassette. Guaranteed to load.
Music programs include random sound listing or
save copy. Add $3.00 each, outside U.S.

Mail order only.:

William Don Maples

688 Moore St.
Lakewood, CO 80215.

Ear Input Circuit

James Dowell

I upgraded my ZX80 (UHF) with the
8K ROM and MicroAee Video Upgrade
kit. I had no loading problems while I was
using a Sears tape recorder. Later 1
procured a Craig tape recorder as a
dedicated component of my system. Then
my loading problems began with no
apparent permanent solution.

Upon inspection of a defunct ZX80
(VHF) with supposed loading problems. I
discovered that Sinclair had made two
minor modifications to the ear input
circuit. One was the addition of a .Olmf
capacitor across the terminals of the input
jack (RFI filter). Removal of this capac-
itor restored the loading capability of this
unit. The other modification was the
addition of a 6.8K resistor from the
connecting bus between C12 and Rl to
the +5V bus. Installing a similar resistor
in my original ZX80 cleared all of my
lnaHina nmKipmc and ureatlv increased
the dynamic range of the input circuit.

Problems in ROM Changing

Herb Homung

A common problem which occurs when
replacing the 4K ROM with the 8K ROM
is that the computer does not turn on
every time (or even at all) when it is
plugged in. If you have this problem, you
can solve it by soldering a 33pf capacitor
from REFRESH to ground. That is, solder

the capacitor from pin 23A of the expan-
sion connector to the ground connection
of the RF modulator (case). Keep the
leads as short as possible (see Figure 1).
After performing this modification, I
checked to see if the 16K RAM pack still
worked and it did.

Expansion connector

Figure 1.

Pin 23A (RFSH)

Component side

Solder 33pf
capacitor here

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